In what ways is the word “work” as mn ;4dru/p u; q3y0ppjused in everyday language the same as that defined in physics? In what ways is it di;upp3 m/dun; rp4 y0qjfferent? Give examples of both.

Can a centripetal force ever do work on an object? Explain6jzg0 lc p8p,v7sf(e l.

Can the normal force on an object ever do work? Exp:.d ip rhq0c1klain.

A woman swimming upstream is not moving with respect to the shore. Iwcaamw6p;vx3si- q,,s she doing ,63 x;swma waq,vcpi-any work? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative?c 6eaj /sztre7,d,oyr++9hg; a ewtn . [Hint: Consider what happens to the dishes when sh7/ ,c gratoaezr 6y. j+de+,n;t9ewyou pull a tablecloth out from under them.]

Why is it tiring to push hard against a solidu9 2kc mwe0o5k wall even though you are doing no worce u90k5m2kowk?

You have two springs that are identical except that spring l is svt, ;)wimnr zk 18vl7ltiffer than spring ztw1li8n ;kvv7)m ,l r2 $(k_1>k_2).$ 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 fnh:,;jh v;sljdj2j tlk43u/ dorce on a block that is free to slide on a frictionless surface (Fig.6-30). The block starutj2;4js;vh3d /jjdnk,h l: lts 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 gravitational pot9 +pepl new2g0g67hl m, eli)dential energy change when you jump as high id+ehn7),ew0 9e ll pmp2gg6las you can?

In Fig. 6–31, water p.j7d (j musm(vb )f4eballoons are tossed from the roof of a building, all with the same speed but with different eu v(p7( jfm .sjd)4bmlaunch 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 lowest:jy3 h cwp-dwbj9:) nf point in two different ways (Fig. 6–32). fw:w ybj):3n dh-cpj9During 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 cause 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 the sprin. zo2ufnc6 , 0v n9jl htabo* c3886tjptv7iuog by pressing down with your hand and then release it, can the spring leave then*a6 locit.o3vt2uzt6 0 ,cj8n h78p9fo bvuj table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The inhxvtmlyd 7h(,1htf 3/ structor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball with7dmfthv/ ,(h3tx lhy 1out pushing it. Why?

What happens to the gravitatzl-jb vz0na ra86nl1a1+4a hiional potential energy when water at the top of a waterfall ljz 1a6b1+8r aaivz 0aln 4nh-falls to the pool below?

Describe the energy tra;t 07gnae t( +kuhwr4pnsformations when a child hops around on a pogo stick.

Describe the energy transforqe.oit,7 lr au0z. .fvmations that take place when a skier starts skiing down a hill, but after a time is brought to .lo vuzer.it.f q0 a,7rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at tu0wdk1o rmq13-k; zkw he top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no fric;mru3-kdw 011okqzw ktion, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step .b68 pr8cgy hmover a fallen log in their path rather than stepping on tophygm8c8. r b6p and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the o:)d .69hm c 2bwltgbvuther, are fired into a bale of hay. Assuming the hay exerts a constatd lb h:)6g.92bv wcmunt frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms oo nwa 2gxs-4+*.kk/gl jz6cujpq4un- )eyi r; f energy, (a) ignoring fryq .4g 42n+ucgj; * unias p-wz-jekxlr/6k)oiction, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a hb 3od:u4qc ui68rokq1i*j 0bx eight greater than its original heqibx48u odk oib:6uqj30* r1cight? Explain.

Suppose you lift a suitcaseod r kb*rx 2o,u9 t7er.wkl64:we5rel from the floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or awk x5e6kdt r .:e9eo,*l4w u27rr lorblong 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 the power needed rather th f0o8gouek+5bd*agnc9hy,lkf ,; e. gan the work.

Why is it easier to climb a h56n1ks7frl+ m vim/wmountain via a zigzag trail than to climb straight upsfkv5mil r+m7/ 1n6wh ?

Recall from Chapter 4, Example 4–14, that you can use wc7,rn1rqd0t3. y1kvwrb ;zia pulley and ropes to decrease the force needed to rr 1r3itrkq.vd0 ;7y,cz 1wwn baise a heavy 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 w f) u0sfay-/75qbavr.g lb/apnf7b7lhen a 265-kg pile driver falls / p5brbfs /a.7lg 0 fu77bf-vqaaynl) 2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high2ne 3( 2pmlei wiokso 4,0m7pn. How much work is requi(e2 4omswml32, 0pnoiek7pinred?    J

  A 1300-N crate rests on the floor. How much worn0 3nwcqic-q 8k is required to move it at constant speed (a) 4.0 m along the floor against a friction force of 233cicn-wqnq 0 80 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 8ygey j/h3ji,c-vs*, rh ffnah0fq -6160-kg crate 10.3 m across a rough floor without acceleration, if tfe8h-,yj3icjq y fg*hv/-hn0f s, 6r ahe effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerat-b3-)o+aof,enqg clz ed by a force across a floor at a rate of for 7.0 s. Findq -lbfa3n )oe+cz,og- the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat ofzl7*q,7,:gfqnw z3 p sw9li.qg q ts11kl(son a table. How much work is required to stack them one on topz(sq7. qq3silzq91 pos,k l:tfnwl g1,gf7w* of another?    J

A lever such as that shown in Fig. 6-35 can xa,j2ja k/)t2jhiw +vbe used to liff objects we might not otherwise be able to liff. Show that the rj,2a xt/j h va2+)wkjiatio 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 k eky8,+mu xry p-..uxixzceil/ b)33 a 28° incline and is kept from accelerating by a man who x xye .i,k+p r/ekz8 c buym3u-il)3x.is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(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 acceleration mo a9e55erdm oc .3hey-no5 lc;r6ng0 of 0.10 g upward. mn oc.ny6hrmea r9;d-e50 c 5egl53 oo   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 distance axjqbd7(n;n l -nis 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, varies as shown in Fig./v/:a4z::mrkc7gjqc pppw2 g 6–37. Determine the work done by this force to move the object jcrpm2:g/gpa: wzq/pkc 7:v4(a) from x=0 m 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 a2c0 bv+3,f pzvre( nihkr6qg a3* +xpv particle 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 molev:.t5fj/aj2eqkfg1j a x97bfcule, 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, by wprng9u, gsaa f gm/(48y)y iz1hat 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 requiredttdc)0j yh)j6.4 2)st ufth. krmf8a q to 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 stop a 1250-kgcar traveling at 1;sdzf0e k mikmu+/o0 zud+t +105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose strin+a jp u0eca13)gcdwm2g exerts an average force of 110 N on the arrgdapa3m0 wc)2j1u+ce ow 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 backwa*vb2c +6i+tnzwid-a lrd 25 cm when the bz+2*+ avtiic6nbwd -lall is caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what fact* x1v 3 ye2puzacjy3r.*pv.fpor will its minimum braki.3 f 3z.xpyp2*eray*v uvj p1cng distance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level.n1mch q(kq:2qxgu g ; road, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the s: hu (mgncg;1xk.q2 qqpeed 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 hf46zc t kfqo,ws;9f 4ziua.8am f96h kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is,qt4o.w8 6 uma99s 6h khifafzcf 4zf; about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who doog7mah p2p 9o0es 80.0 J of work on it? Nph o 0oa7g9m2peglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration zy urlb1ay3i;n,1z80pdxo j+ by a single cable. Det;o1yx zilu ,z 1d8b3ja0nry+permine
(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 stiffness b b5v8kpplq ay 6 06tw,jtp0.hconstant, k, of 440N/m How much must this spring0pavy6 tjhb p560k. qpwb8lt, be stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch.yn 8 yn:kc/zmpu)d.v to another 1.2 m higher. What is the change in poted pm 8c.n:.nukz/yv y)ntial energy?    J

  By how much does the gravitational potential enern gr6 s)y0mc9goew(ic(c hw6 )gy of a 64-kg pole vaulter change if his center of mass rises c(6yc gc9(sgm)i)n0r6whwo e about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has g6 )fw44dqt5- sr2rhhu )iudv speed v = 65 km/h when it strikes adr fugs45dh)4h6qw)t 2v iru- horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is km f*i,z 7ifsz y2wcza 4s4/jsygoti, f)z)792.20 m above the grounif 74isz o)m2 cw4f)zgz y,fzkia yj*,s7t/s9d. What is the potential energy of the book relative 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 elevati zlcc;fcss)m0cvnyw,j.:1 8 con of 1600 m and climbs to the top of a 3300-m8, ywc) v0 c.fn:sc1czjs c;ml peak.
(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 verticalslvxvk,w5rj -xrf x, 31bm-d:ly next to a ruler. The end of the spring is next to the,rxb1v 3xdkx- vlf-mr,:j5sw 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 up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) anj8zqr xs.+o uo ,cl)6vy l)a6rd grabs a vine hanging vertically from a tall t8zcru q)x)ojoa.s+66lv r ,lyree in 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 az 4h7;6 x x/0, kgiocr2xm no4gy8gzpdown 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 uvkcs(-: 8bu50y6 i1d zrwlfxa shove 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 kinetic energy is transp+2o v3azpz4a zz .ag/formed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to .2oaa3a4+ zgvzpz/p zlift 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 jumps verw bpuzh )-:ycjp8gov0 .wf7 a1tically upward from the top of a platform witv -j: .ay8cf 7w1zhw gp)upbo0h a speed of 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 9w2y.m2izfn:z (aje( f 50N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg2z i ym(.wjfnef2z :(a 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 h- dhdq/b.8friic47o friction along the looped track shown in Fig. 6–39. If the block is to remain on the tq /78.hfb4hc do-i drirack, 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 7zw(.5sjiubha ai66xend of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial displacex zsa7 u6wj.i bi6(ha5ment $x_0$ 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 from a bridge. She is tied to a bungee cord whose u(ah2 zl5rs/rwf ip7 4unstretched leng (a7r5fs2phz w /r4ulith is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness 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 ygvmffna 41fnku+cpy *68o.( in Fig. 6–41 is dragged up to point 1 where it is released from rest. Assum4fmpufo+y na1 n*6fcv8 (g.kying no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angle of 9jmx+j)x ka -w33 $^{\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 a spring to be placed at the bv6am0jf -nmc +ottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, ca 0fc+nj mavm6-lculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration 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.wm1 sps49 + o*3uzonnk8 $^{\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 and traveling 95km/h in; *vl+0l-7m im obdghe opposite directions, collide head-on and come to rest. How much the7 *bomihl+; v 0-elgdmrmal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom wqmh 5z. lpflw 0k 8*ym tq+;a6khti/a,ith a speed of 2.2m/s How much thermal energy due to friction was generated in this ,+wmlh p h mk0iqft;k.*qat58l6yza/process?    J

  A ski starts from rest and slid .y4;ec ukp,v zjsuqyn9p(-lwqa3 +(wes down a 22 $^{\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 from a tree 13.0 m above the ; uxm) unp mgl+akc/ x2l57l0+0xdbrrk+m9fk 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 bounces back to a height of,kqm i28 ob:25aawjdntc le:( 1.5 m cimjkaw82d2oe: (:qalnb,t 5.
(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 acrossmv4qf v7loxqt;1 e 4 +2orfeg0 a floor with a constant horizontal force of 350 N. For the first 15 m the floor iq rqe;x442+ 7ft0v1o femglv os frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speezw3 cbhh2 q.+bv hhsgla2f3) (d of If the average force of friction is equal to one-fifth of its wfwhbhs a3v 3g+ l2(.hqcb zh)2eight, with 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 steady 1 bjr32r6ie +v36efcsm 8 lt9ip vto)fupward 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 attached to a very light horizonta8lwet q s(9,fmxv29mql 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 p (q 2 vt,9w8smmqfl9xeosition before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spring, Fln z/zmqi o) ,,v0yu/wa 7r+wrdip26iig. 6–40. The block can slide along a table where the coefficient o 62maw nzrd/v iy)iziuwl,7p 0o+ /q,rf friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring 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 e5y,20ro0x zz:ljvo:e 5mgaxw/m d1gused a “glider” (mass of 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 ,xawz1zmel5v 2: ojed0 /:xg 5goym0rhave been 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- n)o7 t(uosl;xW motor to lift a 315-kg piano to a sixth-story wind ntx;(uo7) oslow 16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what mus;)3 4t thflzxnt be the average fo f4zxht3nt;l)rce exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car acceleratesqo,f 5kjf.i;j k1x)xh from rest to 95km/h in 7.4 s. What is the average powefox;5f .hkj,iq1 )jxkr delivered by the engine?$\approx$    hp

  (a) Show that one Britit v k*h9sir) (ap6dv:ysh horsepower$ \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 oftenot a2sg.-ol; m expressed in the form of “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: k5ak ut8gi8j. )uota about 6.0 s on the level when it is in neutral. Approximately what power (i k auto 8gt8aku5.:j)watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 7wyc(pxd v9 0kh? $a\times10^b$ J a =    b =   

  A shot-putter accelerates hun89f + rbbfo:8v n2va 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what aveb unbfv+:hf 8 n89ov2rrage power was developed?$\approx$    W

  A pump is to lift 18.0 kg o9xg1(* efrmfl2m/vd39m ar w 9zo, qbwf water per minute through a height of 3.60 m. What output rating (wa9g9 w rr zvqal3om d(xmm */,ef29wb1ftts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the wavv n):v gm n5lo(:e *l4c3oystadium stairs in 66 s. The stairs are 140 m lo) ven( 5wgll *3y: v4a:ncoovmng and inclined at an angle of 32 $^{\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 ay2g ;15hizkus01peysr g 0kq 2z6/ofr 6.0 $^{\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 maximum power oupqrn5-b sa; r)4ui d8utput of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional b4; usp8r uqda)-r5in forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg keg 4(f7gl ;4i4joj nnbox along a level floor at a sp lingfj ;e4j k(nog447eed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a g,*x2iu 7l wfv7.0 $^{\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 “5mi/h(8km/h) bumpers” thak g.li4a*8d lvt 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 compression 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 v*4 a8g.likld into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, and the remainib,pn9nx qc/p:-g7 jun (7udmjng four shelves are each 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 layinp79 jn n :g7uqmdxp(-jb,cnu/g flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 +a6xt-6 5 vb(cpdz zpgOlympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was travelingg p (zt6 d-vxcb6a5z+p at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the loog6g cg)wdh 4tslrj ;,2ped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of radius r 6 hd rj,)gggwc42;stl.
(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 air*a7e*no zc ,hpw,z y,jcraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with on ,p,**njye7z,cho z awly 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 a horizontal cord of length L whose other en 3up h7racal7:zyya4+ d is fixed (Figahy aauc z:l77 r3py4+. 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 of a 3700-m-hig: sxdvh1y10 d95vkna hh mountain. The climb is made in 5.0 h starting at an elevation nx s5:v1kdyav91dh 0hof 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 a 920-kg elevator is 28 m above a huge sprif ape)y*st* i)ng ($k=2.2\times10^{5} \mathrm{N/m}$) 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 csed8h,h3ybp hku- 1y;hrf .x6an move 47,000 people per hour. If the average lift carrir.huhp 6e dfb1s,-8;h y y3kxhes people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls verticallsugj( c/-0bkv y 81 m before strikingu k0( bgv/cj-s 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 wiemcu (l5*cr.wq b:2qpth a circular vertical loop (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 fricepqlc2*wmq:5 r(. ucbtion. Show also that as long as your speed is above the 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 ;+nmnyi0:x xqb(k3a gcould convert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fuele: i(am;yk x0qxgbn3n+d 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 upward angle of 45.08wzy7cwk .nvj(8a 1n+bh+k3 0qijzkt $^{\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 insi58)npatab.*+g s :f4jg ujwrfde the scale compresses 0.60 mm, and t8bf +fj4 pjn.s)w : a5gu*ragit tells you your weight is 710 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 grabs a rope, and swings dxef5: rhrz 0e2i;l 2uout over a lake (Fig. 6–45). He releases the rope 2r2i5xe :e0z rudfh;l when his velocity is zero.
(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 climbi) ,w4hs i ry)-l-g ptuf5+9:)idxiug8jlsu fs a vertical distance of 5.0 m in 9.0 s. What minimi)s:xfiuu gdlifp j +i-, 8sl ru5 w-)y4g)ht9um power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water i(z 6djjfb 50ubw:xt8o s pumped by reversible turbine pumps from a low to a high reservoir. To store tht8jxz w5df(0j6:b boue energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$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 halcsy.*jl/gu2qc 8 r2gcf. What is the spring stiffness co/c*2gs 8cyrgj luq2.cnstant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m 8+k vmf3duhci +-.zknup a rough 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 accele7)m(ben sxm zc9f*1 :kx5czcwrate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the sa:1x9nc7 zw(5k zfc*c eb)msmxme, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress tesgv 9 dtrw3wyth,;t/6qt”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an h 9tvr tt3,wd6g;q/ywangle 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-kg rock vertically upward ngli6nday 8 94l r*zou9)p9oq a distance of 500 m, what was its velocity when it left the vo 9 narpu8zdg*9yi6nq9l4) ololcano? $\approx$    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 rate of 9c;1n wm8 z-qnaq2 sv9h5kg/s (a) If this water wheel is set up to providen2s w1z9-nhq8acqvm; electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s