In what ways is the word “work” as qgu6cplyxt7 -7a6a *wused in everyday language the same as that defined in physics? In what ways is it different? Give 7q*l6ax67cy -autg wpexamples of both.

Can a centripetal force ever do work on an object? Expmbfx1 )() b;2 vkrg 0pf)xdusflain.

Can the normal force on u/yo( 9y8wz)oo4x:o8( hacz pqqo(o u an object ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore.n68 5hf b 5lnt,5qgfxq Is she doing any work? If she stop,5ng8qfb5x5l6 t nfhqs swimming and merely floats, is work done on her?

Is the work done by kinetic friction forcesnpej e60ac w6, always negative? [Hint: Consider what happens to the dishes when you pull a tablw0e 6cnj6epa ,ecloth out from under them.]

Why is it tiring to push hard against a solid wall even tho y8av *x/kk2kief 374j4n y*weust3v augh you are doing no w3 24s3a78kknvy kjif 4uax ee*w *t/vyork?

You have two springs that are identical except tlu96lg lmv-j .hat spring l is stiffer than spr l.9j lulgm6-ving 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free t/cd: mxd; kte8o slide on a frictionless surface (Fixdck:em; t/8dg.6-30). The block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitatw,1b08c *t9:t qx74t ymlsuwiwnc 7cxional potential energy change when youl 1iw7:c,u7m8w t4s cbcq wnx0tx*t9y jump as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all wit ,-llud )2azbqo(jnqia hq2 b) 7if.;gh the same speed but wlbz und( .,-o q2gq;j7) lhfbi 2i)aaqith different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its am2vd(e6 l d wee j( u9kl6fu+v/nra83lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will caus( dvekv286 +md9w(uef 6j3ela n/ lruae it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress x0va5s+w))tbusl6jivv+ l l8 the spring by pressing down with your hand and then release it, can the spring leave the table? ix+) ba l8wsl)s5u6tv0l v+j vExplain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33)m.j,g8,h i* jew cd6;ufiorfp, nm9f +. The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor iw8p+d9i cu mf 6f iojme.gfhn ,,*,j;rs supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy guf*f 7rsg4) hj( ccx1when water at the top of a waterfall falls to the pool beljs grc74 xff*h1 g)(cuow?

Describe the energy transfocl3qksj lh:bt.g *n10 fxt. q/rmations when a child hops around on a pogo stick.

Describe the energy try3sd .ltfg:a im)gqgk5avhik +4 05v0ansformations that take place when a skier starts skiing down a hill, but after a time is brought h40k3y55mg+di)kavqs:itlgva f. g 0 to rest by striking a snowdrift.

A child on a sled (total5)ism eovb47g mass m) starts from rest at the top of a hill of height h and slides down. Does the velocit sv4i57eg)ob my at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step (de547ehu /o7p3ereej+y j ru over a fallen log in their path rather than stepping on top and jumping down on the other side. Explae(u u+y/ jj eop7 eedr43r57hein.

Two identical arrows, one with twice the speed of the other7a *exr/vqhtg,ma. 5 h, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the r.5 hhemv gax, *q7/taarrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simlck8: hcp o24gipxkw-og;6 -ople swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to b hk :ox;kw c-c6io42gp8ol-gpe wound up.

When a “superball” is dropped, can it rebound to a height greater xb g /z eaag8 ,7:0lu;mok;sq/6pljhn than its origi7: /x ,j;k/pg0g;aum s nozah6blq8le nal height? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on thtc g70gwk,k: g8h(ib fe suitcase depends on which of the following: (a) whether yg7b8:f kkwg(ch i tg0,ou lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for thf(q).)u2m;+dg lra kri y d0mye power needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb str1emx3gw hp2s 3aight up? e3wpxs3 2mg1h

Recall from Chapter 4, t.th)a -v26pa9 rq)mzja1 k)rv/zu4w j a8 osxExample 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heakoa)-w/p z4uxq)m8 j v2a1jrstt zr6)hv .9 aavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force wh+p.54jyv zoq.ms w im4en a 265-kg pile driver falls 2.80 jqi+vwoysm. 4 54.pmz m?    J

  A 65.0-kg firefighter climbs a flight ofwxyop+w6nlbe * 8zl4; stairs 20.0 m high. How much work is require +w*zwob4ny6xlepl; 8 d?    J

  A 1300-N crate rests on the f(dbh(7fjv)a/i9z m(o/,8isrw xdpp floor. How much work is required to move it at constant speed (a) 4.0 m along the j zv7hr( fiw )(,pd/8(9/ dpsfxaiobmfloor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushingk3d. v zd56lkx a 160-kg crate 10.3 m across a rough floor without acceleration, if the ek5kdd.l3zv 6x ffective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is a 9p/ft- s2f 1hyd9bsxaccelerated by a force across a floor at a rate of for 7.0 s. Find the net work done on the boxfayx9sh-pd9 bt21/ fs.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, liejggn jlhx88. :w7rs8j flat on a table. How much work is required to stack them one on top ofxj8lr 887.gjjs wng:h another?    J

A lever such as that shown in Fig. 6-35 can be used to liffvm.w*s/thmld0:m4 vu objects we might not otherwise be able to liff. Show that th w.4 :mh u0tldmsmvv*/e ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° inca3o 8bhp0mag+1 4myklline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calco 1ag3+pa0 m4kbhym8lulate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M an acceleratioq;0nx7tqp n( 9qp/,c za ze,3zr1zxden of 0.10 g uxr, nqpcp,z9ztzx( 01 /d3ze7; aqeq npward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume the dis rwf8-lr.,h6wwsfv3im e:m7dtance axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, vari8iyxxwip 09+ lzvibi-g/.m ;l es as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m /iiip0.v9l -xim8;lyg +bwxz to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a ukvha (am59rs o2 dt10particle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, x y +np+2hg7cf vy1qf-with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, bmcf* rc6 lc,) qxj gp04fp8-qay what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to )p-g 9(5 coinb:mcxqvcfn+t /stop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop3+3jduzj y7m;0vgmcex e ,iey 7+vp5p a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from i8l1*o)d-a9z7 n dykh t1tzs+h:w suoa bow whose string exerts an average force of 110 N zn9shd+zwu1ok8:yi 1ho7tat -*dsl)on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 rgsh9z w:p l: vi/7wd)cm when the ball is caught zw7wldv i:/r9s)ph:g. What was the average force exerted by the ball on the glove?    N

If the speed of a car is incrq o(c w u0ic:p:r9 vwxe477oygeased by 50%, by what factor will its minimum brakin49yo wv7:co rg7x0euq ip cw(:g distance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measur8*;5xu kjgm ih;9 nhfwe a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic frictioh jn m*g9x58huw;i;fkn was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is p6z q eft*),ne-ztpri:r2vt(ritched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistrz vf-pr*t)t( e:eq2i rz, nt6ance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight uppfaqcbk)2n-bi+7 k .mn+t 7ml by someone who does 80.0 J acl -m +pq 2tikfnb7n+7b)m .kof work on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a sine4( s:qo/wvwcgle cable. Deterwweqc /:vso (4mine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffnesq2pis0 zfg-3 xvoy(w -s constant, k, of 440N/m How much must this spring be stretc02g ypqwfo (zv3x--ished to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from ons:pfb) .) kqbje branch to another 1.2 m higher. What is the change in poq )) pbkfjs.:btential energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vab(q.xoon5e5.tx6zje +; kjhpulter change if his center of mass rises about 4.0 m durin5o..x65jqz ;xe(to nkb ehj+pg the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = : y6yxe(9ks ,z/tup8jw z7ppm65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What ispp, s/6(y ep987j umtzzwy:kx the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10z:e-cs-b r.oyg)ew4u -kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the book relativeso.)e: -4eugz wrbc -y to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1q j;7 +hyirt)0fk/ t yynph39j600 m and climbs to the top of a 3300-m pet n9)qf j7;0r3iyy/ ykp+h tjhak.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertical tz868j a +wf)mgwcwy4w)fyh8jb8l /yly next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line ) hcygz8wlt+w8)f wj8bf 4/a8jwyy6mup with the ruler marks?    cm

  Jane, looking for Tarzajl .vrtb*m.8m+,qdjhiug+t:9vye tz:es* g. n, is running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree ini.gzj, 8g *m .yst:m:vhu* rltb.q+je+e t9dv the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides dowlcsf tq*wmo;1s0pkqc+1 6( aa n a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shovd0/u lg9p gxz db9w.k9e up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kine.ra xh2- 9dt nffewi6;tic energy is transformed into gravitational potential energy without the aid of a pole. With what minf6 i entw-r9ha.f;x 2dimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jckoj 1-ugk 0l.umps vertically upward from the top of a platform with a speed o.ok kjc-u0 lg1f 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignore its mass), whose spring stiffness constant is 950N/m e0;g7u yyd otu) 2pdx2is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-k u 22gddutoye yx;p)70g ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped track shown in F pcpg: as1kmr. 5s8nkf/aif 1+ig. 6–39. If the block is to remain on t: pfknk1gfsp8. rc as1/5mia +he track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffness conslaxez9126a f ntant k), Fig. 6–40. The bloz12xa6fe9n la ck is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps f()w- gr 5eowy 8x-hgoadov6 7x4mn/xk rom a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring s)n6o mywo vr- /edkg wg 4x5ox8xh-7a(tiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 where it iwfqx(-dvmu 2; s released from rest. Assuming no frixwudm q;v- f(2ction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed oqmpxy k2 .n1lalv:.v7f 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing 8q t rax+nvq,4dr9oje 9h.d a9a spring to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an aca .h949 rvaxq,d+n8jedt orq9celeration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a 7.8)a jprs3.tck2 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg a/ocq mz;d..) l 4sh kxeu6 j3p0s.dzyind traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy ix 0 ps i.c6dd)yj.mos.qz3lzh ;4/e kus produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slius(welndr5z o3zd. gi9+m9. rde 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in t9 z. uew (goir+3d.rs9n5lzmdhis process?    J

  A ski starts from rest and slides down a 22 nk3r /b:more48 zp-u4p qje9s$^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped eyrch9+8 ab8;b ik /ljfrom a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bouoss3y76w/jm v gjd9tmxy:(5 v nces back to a height of 1.5 m. vjo9t/ygm 7v3:m( yj sw5sd6x
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled vog nva +gyjs;k +nf4daq0z9 ff5*d ,4across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final spsnd+v ;9 +ov4f,y5agj n q4ff gk*daz0eed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1t 2bv re6u:0dv (ng4ym with a speed of If the average force of friction is equal to one-fifth of its weight, r:u vtmgv6(b d 4ny0e2with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steadac8nzf b)evqo y54-(o y upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attachedznq 7lhfy4o -- to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping an--lnh 4 yfzq7od turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached l:*vzwd7c j-*q4 iu y:cou9 ntto a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spriuw*tcd:7ulc9 *yq i4oj n:- zvng is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass owr z84 h8 ,+bbblwsyqdiv25/tw8 /tem f 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have bee8 ,tzw5/8i8 hewtd+srb/2 wmy4v q lbbn in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg pxqbp9zowod3 xz/wq/89q pm7xj-l / k1 iano to a sixth-story window 16.0 m abom-x k9qpx7 j/9q z3powb/1wzl/ doxq8 ve?    s

  If a car generates 18 hp when traveling at a stes8b y xm/ 6vn.k5vte)wady 88km/h what must be the average force exerted on the car due to friction and air resistvw.bm ynsvk)t6xe /85ance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What isg*za expt g m9o8q;9l0 the average power delivered by tpqgt98a o0lg;z9 *x mehe engine?$\approx$    hp

  (a) Show that one British horsepow(s2a;fdaf n:y er$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of i2p5clueq 1 r; qf6zo2 gv/-h14oucdd “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h in aboutak5o .7n 6sp)sk-sg xg 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a cons).k-7nksgg5 xp a oss6tant 75km/h.    hp

  How much work can a 3.0-hp motor do 12ncy. xkj;+zzxczs q48 qwm, in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motion tapf waz)x9ud+ txj2q1,7k o*c okes 1.5 s, wh )to zkx2pc,1*9 f7doauqjx+w at average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minh (jghyscl57y( g(ud/ ute through a height of 3.60 m. What output rating (watts) should the pusdugy/(yh cg7ljh 5 ((mp motor have?    W

  During a workout, the football players at State U. ran up the stm tv+e)wk:w , dm5a2nxadium stairs in 66 s. The stairs are 140 m long and inclined at an angle of 32:ew dw ,xtmavmkn)5 +2 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a 6.u o u0mf gjhbmqel0w ,)h5wktj9;m:ku1c8 +z90 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximumt* nfuel 78m25o3ovf -t7w vpe power output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forcfm7of75t3otelp*we-un 28 v ves add up to 650 N?    $^{\circ} $

  What minimum horsepower must a 0+su x,uxq:pxif)-9n vr-b t pmotor have to be able to drag a 310-kg box along a level floor at afv90u-)srpb x+tx-n,i:xu p q speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.d :f8t+ a30 ptgnsn,ae0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “51g:e km0prhhxs8.2t3)gl r y3 wqa4wemi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compressxw8em:1 l4wgg.te3p )k 2syh3rqrh0aion of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the grougfn0 ml4/s7w *enb v zt2s5-htnd, and the remaining four shelves are elvmt7f0t* z hs sn/5-gwn4b2each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympij p2p*z,c-x .cx/2t8 f ruyuvics shows that his center of m2-fc2yp8j .ct zxrup* /ix,vuass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped tri)yxmt1+9 wf iack shown in Fig. 6–39 is to remain on the track at all times, even at 9i+xfyt w)1im the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without his p h8;q *c8 aei:brmaf.darachute opencbrhiaf8eqm. a;:8 *ding. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to 1tu b 0d2-hwyktefd j0z;3t,l a horizontal cord of length L whose other end is fixed (Fig0;yw03u1ldfktjhb e zd2t,t-. 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top ofg4 qq -cqz)4u0wfkaj0 a 3700-m-high mountain. The climb is made in uj cqq-q fw0g0 k4za)45.0 h starting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when *u8ln dl..; / ght9ckfvhiqh8a 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 47,000 per1ns jqqqbeshv08v (hn/ oxw9n:o ;36ople per hour. If the average lift carroqv 8hhr0n63/9 ;q q(e1n:vb josxswn ies people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rat4coif ) kc3b2te of 650kg/s and falls vertically 81 m before strikingt3 )2c4fkoibc the turbine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical looebnf(+rb:,. 7w b +*lxigs) zknd5bllp (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above lbx bez w, +illrk* b5fb +:7dg(.nn)sthe minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into work, how hw6x axl. an8,dgx+/rj igh could an 82-kg man climb a ladder if he were /8 x,dxjgw+ .alar nx6fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an u..zhvp+(30h wydzja )kocud2 pward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale compresses 0.60 j3(+fcvlpxwgda(a nk.)h(9 yv2(exbmm, and it tells you your weight is 71( e.3nkp bjl( v)x +dfay awv2x9hcg((0 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grab - rxw.bbeyv/ e/ab0e1s a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is zero.evy/aeber1b x/0- bw.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance o- nz umjcd+ul;) ((bw:7 c2u:xvjzixbf 5.0 m in 9.0 s. What minimum ( l)uzv7;ujbzxxcj:w i ( 2cu:nb+dm -power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Watf 2j()dbj(n dker is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW k)(bdn2 jd (jf($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What fdyw4,a bt+l3) 5ypqbis the spring stiffness constant for each of the tdabt54,ly+qwyf )b3 p wo resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a row a/ (wngea+h(ugh 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how long wq-gck5n ce iopp/v ;19ill it take to p/eq i;cpn-95g1o vckaccelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardb ,ieot ,;s+rjiac function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg pat t+;, b,ijesorient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-ozkyphfz,/30j xdwyaje99) )kg rock vertically upward a distance of 500 m, what was its velocity wh)x)wp, d30 j9jyzy e9fkhzao/en it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a ratzdq9 u j*6afk a.u*nw:e of 95kg/s (a) If this waq:z.wa9u j fkd nu*6*ater wheel is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s