In what ways is the word “work” as used in everyday lanvuc-gm-/u jbj, :q5r zguage the same as that defined in physics? In whajcv5 -q/ g,:buzr jum-t ways is it different? Give examples of both.

Can a centripetal force ever do work on an object? w7o ys0 7lm l)vrj8xk-Explain.

Can the normal force on an object ever do work? Explaii, gfmt3a0ag ykj*b*vd agt.(7l5tc8n.

A woman swimming upstream is not moving with respect to the shore. Is sh) d5kezy fl6m;e doing any work? If she stops swimming and mdfme 5yl)z 6k;erely floats, is work done on her?

Is the work done by kinetic friction forces always negatio;3f 1dhixdpk* m63 ;nt yez:dve? [Hint: Consider what happens to the dishes when you pull a tablecloth out f 3;yidmop:fz3xn;1 thd6ke* d rom under them.]

Why is it tiring to pua e;qfn;0 efb3/ccu* nsh hard against a solid wall even though you are doing no won; ucb;fnea*/0eq3 cfrk?

You have two springs that are identical except that spring l is stiffer than spr dw t*s*)az*:wfv(nby sdwzyb tavf*w:*() *ning 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 )79mp 2tzv)kocxb 55pw/mfjig *n8 g4cd 3 gwnto slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the c)5tp/ngi84d v 3 jzbf*xm)kgc wo9w5mn 2gp7time 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 potenti4p2.bwm1uqn e 7rai4wrl +xp, rxs+.u al energy change when you1 mr7pubn.xr q xaw.4+espw2rl+4 iu, jump as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all with tmy8l9s oq8 w)n/(td+,iq gn /xh,txzwhe same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistanczinh 8)8gxdystl q w/n9,/wto+ ,qxm (e.

A pendulum is launched from aykg9db0 )sh0*vsjhtsp0vb b 9p/zo +1 point that is a height h above its lowest point in two different ways (Fig. 6–32). During both )1yhho k*pj9v0 0pgtd/bs+z s sb0vb9 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:o:fef c* eln:ya n7z5 on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of e 7:5fnlofa*e z: c:nyconservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–so7x*r bb7(-2cjw2 x9 lxkhjb33). The instructor 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 without pushin*xx cj ojwh27-x b(lrbkb97s2 g it. Why?

What happens to the gravitational potential energy when water at thegd e:,vlr(sw/3dg4 op top of a waterfall falls to the pool b d3wd(4:,v grpeog/ lselow?

Describe the energy transformations when a child hops arous.e 1m/tlh4nand on a pogo stick.

Describe the energy tranfnx)8fq4x lmbgt 82qn4 gd-f3 sformations that take place when a skier starts skiing down a hill, but after a time is brought to rest by striking a snowdrif-d2l t88qxq nf44b g)3xm gnfft.

A child on a sled (total mass m) starts from rest at the top o;4n(lyjzj9 og4 p/hbu3 a2lwjf 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 icyllgj4; ojnab4/pz h yjw3 (92u and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a falleg(: vlxm-qc3p 6rk::yc /vkxun log in their path rather than stepping on top and jumping down on thrckpl6 cx:yx- k3v(q:/umv:g e other side. Explain.

Two identical arrows, one with twice the sf 6b u;z7p-k,jtm of6npeed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrat6-bom f7zfkn6tpj u,; e how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in tb2 t ;vuvy z7ql)+ulw0erms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to be wound upzqvb +0 t)2ywl7;lu uv.

When a “superball” is droppe rzus 4g3l dvl44ckt79d, can it rebound to a height greater than its original height? Expl7 t4s3ul4vgr4ckl 9 dzain.

Suppose you lift a suitcase from the floor to a table. The work you do on the5 rg.f t/oeabqi)p.*hy2: nmu suitcase depends on which of the following: (a) whether you lift it straight up or along a more compli/ atiu*2h: ofr.ne q)b.g pmy5cated 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 neede-12x8ozxo ;m5-noxatb f ck- rd rather than the work.

Why is it easier to climb a mountain vi-m5v3 bf*ln , dn(xqwx11gz wja a zigzag trail than to climb straight up,n1-g w qb(l*dfv1nz w3j5mx x?

Recall from Chapter 4, Example 4–14, that you can use a pulleyahh(01) iz/dbktm 6xd and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the loa b ximd /6dkhz)h(at01d is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-m3icfo5 hrz1(bc bcq4hr) 58ekg pile driver falls1rmhfbiec5 cc(8 rz35ohq 4)b 2.80 m?    J

  A 65.0-kg firefighter climbs a flight o3*6 fw+-zczu5lbwg vu bb8bm:3j7t glf stairs 20.0 m high. How much work is requ3bjcz7v f-lblwb* 6wutmbgz8 :3 g+u5ired?    J

  A 1300-N crate rests on the floon cpx k++gaq;jm18kg:r. How much work is required to move it at constant speed (a) 4.0 m along the floor against a fric;q1g8p:xng+k cajm +ktion force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizfn8 yo27mh k7dontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of fmfy7o78kdh 2n riction was 0.50?    J

  A box of mass 5.0 kg is accel3 ydwfv1*p9n) pgz:gr erated by a force across a floor at a rate of for 7.0 s. Find the net workpzgd1np3v* r: )9 wgfy done on the box.   J

  Eight books, each 4.3 cm thick 4ajy qh2p0o,tzbj5z* with mass 1.7 kg, lie flat on a table. How much work is required to stack the 05ozjqj2 4 *hbyzt,pam one on top of another?    J

A lever such as that shown in Fig. 6-35 can be u p oiq63y1vd :hd7d ibye;o0j(sed to liff objects we might not otherwise be d; dy7 b3oijiyd1( 0 opvhq6:eable to liff. Show that the 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° incline and is kept frz bcx(od,1w t.rj7eq5 om accelerating by a man who is pushing back on it pad57e(1xtwb,j oqzr. crallel 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)wmwapk .ra 3,xd 6nwv7i;vt4 M an acceleration of 0.10 g upward. dia7vv. 6x mw3ww;pr n)4ta,k   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 w-u(xe3xuc-t 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,f; 7s db;oiy3u varies as shown in Fig. 6–37. Determine the work do y ;ds3fiub;o7ne by this force to move the object (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 a particle ac- hwletk e:w:d+z ;qm ouq).d(ts 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 oxygenoe pznpw)(kc.1: bn.o molecule, 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 what facto.grw(3 e ermwm.ws5c27r h ude7bxc-0r has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requirj d h -;yw.azxb5+:8zt-fgiz*wohyl7ed 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 bqc;y 9qwo, la5e done to stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is firedid5wqwcu(+(p: 2ca rp from a bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of t+52wpd r(wp(aicuc: qhe arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s mo 1keuw):jhg.sves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted hew)jgu.1k s :by the ball on the glove?    N

If the speed of a car is increased by 50%, by w 4o3 poxh/xym9hat factor will its minimum braking distance be increased, assuming all else is the same xo/xp394oymh ? Ignore the driver’s reaction time.

  At an accident scene on a level road, inves* +54iu ttin zr1z1 :uyo ,o+ysqxka9ktigators 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 speed of the car when the kr nq y5 i:*11o zzi+o4sx+u9ya,tktu 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 pitched at By the time it re+i7gf 9vl )p9*ojunlp zwa- :baches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance betwee vi)gonj9 ub:*al7p-plf9 z+wn the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if throwdh40zifap5 r6 xgpc37n straight up by someone who does 80.0 J of work on it? Neglect air resistance. ai03 5zcp7dp6x hg fr4   m

  A 285-kg load is lif,( ey1r pa.xvfu ;je5 kdmn,g/ted 22.0 m vertically with an acceleration by a single cable.5f/ypeu.1xk,(j m;rng da ,ev Determine
(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 stuk5dj2zs:e 8eiffness constant, k, of 440N/m How much must this spring be stretched to store 25 J of potential energy?j:edue8 2zsk5    m

  A 7.0-kg monkey swings from onep546 nm awwk1d;wv: hb branch to another 1.2 m higher. What is the change in potential envp bhmd:k4wa ;16w 5wnergy?    J

  By how much does the gravitational potential energy of a 64-ad6y,b *hao5h/ wgifua l*i(ma3u +o)kg pole vaulter change if his center of mass rises about 4.0 h,lobu uii3+fd()* 5wgma6oay/a ah*m during the jump?    J

  A 1200-kg car rolling on a horizontal surfah0w2ns: 9; zqy-zd gylg,25 oapw 0rbpce has speed v = 65 km/h when it strikes a horizontal:a2dlzyqybo0rh pz ,2-gw ng59s0; pw 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 2.20 m aboq8rnlx9wuv 89 kj ga:ar15ej,ve the gro awklgr,vxe jq8:a895jn19urund. 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 elevation of 1600 m and climbsy;t.d6 yp:x5u- xnqet to the top of a 3300-m peakxe.6tdq- 5yn ut;yx :p.
(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 vertically next to a ruler. The end oesn,gcr. cv qep.2 eza/.+:nbf 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.zsbegc cn p.nea:r./,q+ v2e spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vine ha2jda16tk-g4 r .1/ywr keiab onging vw/g61d4rbri 2-jya 1ea.k ko tertically from a tall tree 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, sli zb,k9b0( v2llt 7mmyvdes down 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 shove up a frictionless 28iy.: b l/-1vixt 3dlfg.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 transforme3sa ve*oh5 9*(py3adm 3 vt0ffei,yazd into gravitational potential energy without the aid of a pole. With what minimum 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.t e33 e9,f5 a zfm*h0(asiavy *ovypd3    m/s

  A 65-kg trampoline artist w8x .xgdjp i5k+sm5*pjumps vertically upward from the top of a platform withkxi. dw*sp8 5xg+m pj5 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 (ign2udke q)mv0 gcq3l t;/ore its mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upwartu2; leq)kq/03cgvmd d speed can it give to a 0.30-kg 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 Fig. 6/y1nci1g r8gd mwzda0 m3 1v-v–39. If the block is to remain on the track, even at the top of thn-/ya zr1gm0v vwdcmd1 8g i13e 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 q *2oa/hnryfnu1j( (r(spring stiffness constant k), Fig. 6–40. The block is givenqha jyuor(n /(f12r*n 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 )jrb:.s:ckrk6ho*a1qq y242 ggmytb.ki fk ( from 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 stiffness constant k of the i1gk)cqkh b6qgays24f :.:omt. 2 kb*rj(kr ybungee 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 h/ hr0 yry-1qmel .jc4cd2n2y(dfr6ris released from rest. Assuming no friction, calculate the speed at points 2hdr j r-hrm0 1l.yyyf2e/qcn dr6c4(
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at bew ,dn5p5 k;b6dfhdul0)wog ( wwe+1an 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 a spring to be placed at the bottom of 5pzb jf-p 7r3i*k.2gpnho /k wiyc6a1an 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 acceleration of no more than 5.0 g when brought to resacp 6i/i*.5zh1 f3 ny wpjkb7-pr 2gokt. Let M be the total mass of the elevator and passengers.

  A cyclist intends to c9/w(de ax5a siycle up a 7.8 $^{\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 95+0so*1 ,kkvw +mbdzchx5-ikd.1b erixjm, m9km/h in opposite directions, collide heais5j 1be 1k*i m ,h dwmk-z0ck.++ vbxd9ox,rmd-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high anih4a ed1spozx -c g-/(d reaches the bottom with a speed of 2.2m/s How much thermal energy due /-(zegoa1c 4ix -sd hpto friction was generated in this process?    J

  A ski starts from rest and slides down a qzhd+5 c+qsab-ms p9 +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 40mfpd)xi0j 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 2ca42wl4a 6d7azn r; sp.0 m, and it bounces back to a height of 1.5 m. ; waranps672 az c4l4d
(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 fezr(2,mz+g x/fd kj-rrom rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floorzxrm2,d/ gz -f(jk+re is 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 po2*d b-l0w w ghfscg qqad4/).jint 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed 0g2sd/afq dwc gb.-4q)wlh * jwill it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the e:oj 8obsyz61zcp 5/u foot of a steady 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 attached to a very w a 4lk4d-iis4jb:d .3jf/vdo 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 and turning back. What is the coefficient of kinetic friction between the block and thef44w4a .j:ikvo-d3dd b /lisj table?   

  A 280-g wood block is firmly attached to a very light horizontal spring, F(d iibk2*q)4 ddcnj)fumhro)+rs / ) big. 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 spring is released from this position, how far beyond its equilibrium position will it stretch on its nd(q/cu42jfd)bm ks b)o i* dr +rih))first swing?    m

  Early test flights for the space shuttle useg. ukv+;;r ud0p;b oxvd a “glider” (mass of 980 kg including pilot) tx;u;; +k.0 bvg uorvdphat 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 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-W motor to lift a 315-kg piano to a sixth-x vgbo x.5w,t42-nupne1h y7 k6ky5c ystory window 16.0 m cu46-2 pkbhy7,1ey ow 5xxtknyv. gn5above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must bw :l0wq8mn 97i buujf1myq*,de the average force exerte q1df *w7miywlq 0,:uuj9bn8md on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/hkrb8 2zds8r*s in 7.4 s. What is the average power delivered by the esb*dr82 zs 8krngine?$\approx$    hp

  (a) Show that one British horsepow yx+hr+97ki)fahk: l ber$ \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 “kilowatt-hours.”5:hg+dd(3b+v yjby h h
(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 6sooo36y* 9l38wxbq tc 5km/h in about 6.0 s on the level when it iso8x boc3* q 6o39wlsty in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 07je )o)2j rck1ix ulm3.0-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot (ku9n( btk5/m+ r51lj u avoczfrom rest to 14m/s If this motion takes 1.5 s, what akb5 ok(l/9trzu5(+mj1vnc a uverage power was developed?$\approx$    W

  A pump is to lift 18.0 kg of wasj3 z8 ewggh7j9f ba4:ter per minute through a height of 3.60 m. What output rating (watt3g wf47zs:jej gah98b s) should the pump motor have?    W

  During a workout, the foot; jms qr,bak*iuaerg-/ n(29cball players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at aeca,(- i/; gn*mus2qark9 jbrn 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 qbgu. b:d-,wr3 33fnu pa*48emtjiq wa 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 output gdvw6b. jv*qoro- .. u,wfgi2of 120 hp. How steep a hill can it climb at a constant speed v rqd2w fwj -ogbo.i.g u,*6.vof 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg box alongjv,87iucxm ).sgs oyxu/w . +u a lewm.uvj8 x giuoy c)+x/,su .s7vel floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.0gum6v/c2d6x jxa1yo.reg3 -z $^{\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” that are designedowk) -tnfp 8u/ to compress and rebound elastically without any physical damage at speeds below 8km/h Ifno-8)ktu p /wf 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 into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the gcmcsr gn uz)e aneod-*6 1.-leq01o;qround, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5lodsoe -e0;zmqng * ur- qcea1.n 1)6c 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 1931dlmcxvf(r4* 2x9h7gdhix: s 3 vami(6 Olympics shows that his center of mass rose 1.1 m from laush(iivvhr1 gl x m2(:cf93xx7dam4d*nch 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 fqm vf:czrha /17a 4p(rriction along the looped track shown in Fig. 6h4avrzc qf /m(1:7pra –39 is to remain on the track at all times, even at 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 aircu+;a 25wcpik oraft without his parachute opening. 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 5a u;w2i+ pckoand 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 Lo x*kpe sboyu.5i2amo+,i y z /xq2/z; whose other end is fixed (Fig. 6–43o.2b;o ,i+5/ yeyqip2moxz*s/ zu ak x).
(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-hig9; *wzf(ppnzj h mountain. The climb is made in 5.0 h starting at an elevation of 2*jpz(np 9zfw ;300 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 al 7bab5 cj- vo6;h3ysmbove 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 it 4uzda b,pmlihc dxn 9t oy37m915/-oqs lifts can move 47,000 people per hour. If the average lift carries ped1t/o 57z i-4q xduyo9cmlnhb9,ap3mople about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate olr) by3)l ew-ao80sx of 650kg/s and falls vertically 81 m before striking the turbine blades. Calculate ooleby) )s-la8w3x0 r
(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 witr ,*vsey w;3jawktw 0.h a circular vertical loop (Fig. 6–44), the difference in wt ,3ejr.sv;ak0 wwy* 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 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 could convert a candy bar directly into work4 wmrmljy-q 2), how high could an 82-kg man climb a l-2y) 4q mrljwmadder if he were fueled 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 fire51sd4dfa:rx ,f8cjxz d at an upward 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, i ohqp;+ b01 8/sbluwethe spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the sob;bwe p+ih8/0q 1ls ucale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swin*qp+fawv+;5dramm /jz ajzf 2q9wu;-gs out over a lake (Fig. 6–45) ;* j5jaqdqm9zwuf vaw2f/+ p-; r+maz. He releases the rope 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 climbs a vertical distance of 5.f*vjxz 00uo vm.f:u*i0 m in 9.0 s. What minimum power output was used to accomplish this feat?uxm:f0*uo0*v.i j vfz    W

  Some electric-power companies use water to store energy. vf yzne d86s3-l, 9motWater is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy producedymetn6d-8fov3 z9ls, 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 cvdo3jn ed6,s(p-)x9 rwq 4.u ao tk2ltut in half. What is the spring stiffness consd tp ,-3xneoqakj (29 ols w6dtuv.)r4tant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0z wi4ft0m5s0px m8c) o m up 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 accelerate from 35km/h to 55km/h*k4ye;kai/efot vheg ;sp j-nk *k912 in 3.2 s, how long will it take t;ysvtnhkeo9p j i e4efkak/12g* *- k;o accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for carpgi1km t0z5w9a vqcx;u,d icuk8 43g +diac function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient wcw 5 uxigakz,;pd8g+ 0qv 93kti c4mu1hen 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-kg rock vertically upward a distancf ws9uy( yhs((e of 500 m, what was its velocity when it lef (syw f9h((suyt 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 zjc ) k9:k7epac-a)gj aum+ 9trate of 95kg/s (a) If this water wheel is set up to provide electriciac)j ac7tz+p )jkamkue- 99g:ty output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s