In what ways is the word “work” as used in everyday language the sameki 5kb9q. jr,w- nd9jf as that defined in physics? In whafq -9kkjn 59,bjir dw.t ways is it different? Give examples of both.

Can a centripetal fory q. c+uvhgn(6ce ever do work on an object? Explain.

Can the normal force on an object ever do worzccu ofx4h9xo 9 6v+3fk? Explain.

A woman swimming upstream is not moving with respect to thez:f 4l;n )hoqy0,-qp *gqrqyp shore. Is she doing a,rg:4q-q y o qq)pnh0;lp z*fyny work? If she stops swimming and merely floats, is work done on her?

Is the work done by kineti (cin 67)yovba.b ;mzwc friction forces always negative? [Hint: Consider what happens to the d.bbc(imyz 6o)wa n 7;vishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solitb0wsxh71-k7nt4 i7 c3ehr i:h c,jcfbh2 ou8d wall even though you are doing no w fch3k o bhxej8ib:7crwu2cht0 -, 1t4i 7s7hnork?

You have two springs that are identils 9-a t.s9at6)t iglmc+kjt/cal except that spring l is stiffer than spring s)k lj.ts+-a 9 9mc6/ iltgtat2 $(k_1>k_2).$ 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 f5xuc0;tg20vcefxp2w*w) cr( e0w nd oorce on a block that is free to slide on a frictionless c5ecw2ev pf)xwnd trg;0uow02x*0( c surface (Fig.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 grav2i bbw-ehf3(lf;r8knmu )0j c itational potential energy change when you jump as hic u2b;mrn 0fk 3fe)lh-bj(8 wigh as you can?

In Fig. 6–31, water balloons are tossed ;7l5xp *gmr+mu.smt .t/ aebo from the roof of a building, all with the same speed but with different launch angles.7 egmmm *bpra/ ;.s5t+lxo ut. 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 4gzmxspy:f*qo 0k iwdp)wq36 swt 2p)t1f g-1point 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 initi1)w*:ms) 0g1w p i d og4xpzkt-f6pstfy q3w2qal 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 compress4 qc2hk u3r:vh*5tomg 5ce i1j the spring by pressing down with youg*:u3 hehkr vcqmc42i 1jto55 r hand and then release it, can the spring leave the 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 insza-v bse -kcw7 tv;nu c-9)re9tructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructok tw;9nzve)7cbs9 eau v-rc- -r is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy wrib.g vax6n ml37fl7ah)h0j1hen water at the top of a waterfall falls to t.hr7f xg al3b6ha7 0mni lv)1jhe pool below?

Describe the energy transformations when a child hops around on a pogo.h* fv*nwxz3 f,o ubp6 stick.

Describe the energy transformations that take ple mh611qy5xu vace when a skier starts skiing down a hill, but after a time is brought to rest by strv uqm 11h5ex6yiking a snowdrift.

A child on a sled (total mass m) starts from xkp8,xpo)y d3rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of t xk)dxpyp o8,3he hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a faq hfr8np-o:h44l+3 knvkp dn)llen log in their path rather than stepping on top and jumping down on t-lnk:kn 4 p 84r+vd3nfhp)ohqhe other side. Explain.

Two identical arrows, one with58 k;bcpnwucdma +1 a/ twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on t 1;k5w8pcnac/ dumab+he arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in tera*,tlugxd ( xdxh3c1,ms of energy, (a) ignoring u,3xadtlx d( 1 hc,g*xfriction, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound t+ak5/z4n(+ak j.sx1ir m yk ovb7 7gdvo a height greater than its original height? Expl7+avy1nm ka7(4z+d kj 5 vsrxg. ok/ibain.

Suppose you lift a suitcase from the flof6i j6 w5taggx4 *1fve;h,k yeor to a table. The work you do on the suitcase depends on wht,1 a w6*x6vg;gyekfej5h4fiich of the following: (a) whether you 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 the power needed rather thhp5)+n )9*nq ac zlpyku;x.b uan the work.

Why is it easier to climb a mountain via a-1/zql/ dqrlc3 tzzri g;o0*o zigzag trail than to climb straight up?cz//d 3rlrzgoi *q 1;lz-0toq

Recall from Chapter 6 kv).4) k xfwf: zwjm(o0d /6 tv+nsfku)qaej4, Example 4–14, that you can use a pulley and ropes to decrease the force needed to raise 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 conceptsko jf) fv4ux(a+nqjzkf6w:ms/d 6))e v.0twk.

  How much work is done by the gravitati.tge4ad kk; 5wonal force when a 265-kg pile driver fallsadkt.5keg4w ; 2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much wo 6d,tjjmx4m-h rk is requi tdh6-jmm, xj4red?    J

  A 1300-N crate rests on the fl7l 5j. ya)1nzp74cmgtnr;j+ wzkk, rxoor. How much work is required to move it at constant speed (a) 4.0 m along the floor a xj5j nz g)k7lm.7r4, nc1rkaw;t+yzp gainst a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crate 10.32t ,u2e*iuv/swssvb+7 ko2du m across a rough floor without acceleration, if the effective *t i2vovbsuk,u2s2 us w+/e7d coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force a)l)kh .6kdgumcross a floor at a rate of for 7.0 s. Find the net work done on the boxd.ukm6hgl )k).   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lipr5v egtd30. pe flat on a table. How much work is required to stack them one on p.e5g0vtp3d r top of another?    J

A lever such as that shown iqngqv(.ok :* hn Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of output force *(ng :k.qohqv, $F_{\mathrm{O}}$, 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°,p7)ul wyxn (vpm (aq3)vaw,y incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36m)apy,(aw7(wv,pxn uv)y3l q). 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+1 myl9 at);;kjdoyzt;mebne3 ; cvn4 acceleration of 0.)jc btzn1m+dlak;mvtoe;9e 3y; n4y;10 g upward.    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 axissph24declqlk1/ j3 0 y 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 5 tmdu gu1 2bph5gz9k91wnsoea1.ne7,lb lt, Fig. 6–37. Determine the work done by this forlunu.wahe9,7b k b ezm g5ol5,1t n29dspt1g1ce 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 acts in*cg* xw hn0v/rewp;6e 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, with mass of s8y:j n+wqhm:2i6lg w $5.31\times10^{-26}$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 factor has its spee**p;e y)/o uw;kuoa rpd increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an electron l3a++wb7zruiu(8h5pi gl)/tgd9j nk$\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 travet-jk+hayk .z a 4if89lling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string c+ akahcw*-0 vexerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed avk0ac-h*wc + of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) t w fj0drgqc6dtwn yeb2(e3fwf.,2:3 iraveling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ballt2e.wrwy cf ,idbfd0:j q2f6w3(e3g n on the glove?    N

If the speed of a car is increase8unjg nzrhop r mp:, g:3g07*cd by 50%, by what factor will its minimum braking0g7*zm3n ,pr8gc ogphj:nur: distance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene( md)+trf4kdm jaou ;08aw ahv3xg9y*v7jnv1 on a level road, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day,vudmyw80(j 3 akvh a dxj17*r;4navot+f gm)9 and the coefficient of kinetic friction 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 pitched at By the time it reach59ekxz2x 7brvgu:x +g es the pl7uk2rz:bg gvex+x 5 9xate, 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 about 15 m.    N

  How high will a 1.85-kg/oo b(z:ng; yw rock go if thrown straight up by someone who does 80.0 J of work on it? Neglect air resistance.n; og(zbywo/:    m

  A 285-kg load is lifted 22.0 m vertically with an au aydg7.s84yycceleration by a single cab4.a uysgd8y7y le. 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 stiffness constant, kre(dk0o ndw 76,ip8 vih3 o)sy, of 440N/m How much must this spring be stretched to store 25 J of potential ensrk0vwd 8 h(3d,ip n7ie o)6oyergy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m hi-d0+yk dmx6g 0 o3gniagher. What is the change in p6+0-yg3mx dkoi d 0ngaotential energy?    J

  By how much does the gravitationq.0,:ra: 6p .ye gnbtqo44xts iz vlr5al potential energy of a 64-kg pole vaulter change if his center ofp grzn6.ql0v,xey .sar5to4 it:4q :b mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a hop6d7v3 up s4 yt9e:nw ptwt2(urizontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a dw9e6 3td2uvps7:p n4ut w(ptyistance 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 above : v8;am os+lfgthe g8 sfgma;+ov: lround. 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 elevata*oqk6 br gpr;0l:6urion of 1600 m and climbs to the top of a 3300-m peab6 lrr grqo6*u ;a0k:pk.
(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 = 53nh6dubi*im +9 g(w eh9jg /q-jN/m hangs vertically 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 attacwg9/j -m+gnihqe9i b*dh u6(jhed 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 runninmpgxt:i gods t vy8n3+7s-0y :g at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree 0:m si tyg7s3oxpv+d g-nt :y8in 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,ni qhk6:m 8y2z6a0ptxz l m27g slides 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 frictio*mw f/ssa pja n5(8rage ;-p5knless 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 transforme o jdzyc9,,st, dnfd85d into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift heynt5d z8 ,co d,f,jd9sr 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 verticalltfw31+w a7ny-bwfqs4t rnh- 1y upward from the top of a platform withwtn+3 1fay- s -14r htn7qfwwb 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 chsoi* 9d+s:gg onstant is 950N/m is attached to a table and is compressed down 0.1509h *sgd:os g+i m. (a) What upward 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 trac5 vx5y*4dmi5kuvkp3htvg k+/ vs/m(sk shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h musv m/5k/vyh45k+g3pt uv (v sxmks5*idt it be released?    r

A block of mass m is attached to the end of a spring (sl ,sn+nm9bu )upring stiffness constant k), Fig. 6–40 um )bn+9usn,l. The block 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 jumpa4hjd- u,w o3ocpr vsf /t1*b.s 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 bungee cord, assuming Hooke’s lahd1o,j rsvpf3.*a/t u w-c4obw 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 draggedmah8vxwc*d 3s3 ug3c* up to point 1 where it is released from rest. Assuming no 3 cu agvs*83hw*dm3xc 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 /q5p84j3;k ogm igge 0u8jzmh/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 a spring to be placed at the bottom of an eld8o ;/vwto9p:3ui mmdevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculwuv3 o:;i9m8m/tdod pate 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 cycledo85 :o9vitq :fa+thd 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 iy f140momuiou72 e3m traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collision?ioi 4mm2emu0 17 3yfou $a\times10^b$ J a =    b =   

  A 21.7-kg child desc / x byo3pc63ybpxld8-lp5l;jends a slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generatedp 6- c ly/38d 5lbppybjo;xlx3 in this process?    J

  A ski starts from rest and slides down a 22 9nl jlpxki ll9. wopsn(;0d(0$^{\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 ground. aj (q iut-7k-xiaq 68.gu.zgb
(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 bouncesj7a;u7q c1 /xcguuc0c back to a height of 1.5 muu7c 1gqaucjx0;c c/7.
(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 xj*p0(fw+)bca ph7 b/r xe(kt across a floor with a constant horizontal force of 350 N. For the h7fc/b ( pbxw)+*ke0j(a rp xtfirst 15 m the floor 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 point 1 with a speu1p o)i(thre0 muqxr-t (-7zapyk83sed of If the a 8kx- ) (a3o0epyru hqmti-p 7ruszt1(verage force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reachsycbnf6pf.kg.4s/nn; i5 )+j z5 quzftyj* 3yes the 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 ligh *yuz c9ckvzf +g.j-,st horizontal spring (k=180Ncy+csf.,jvgz uz *9k- /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 the table?   

  A 280-g wood block is firmly attached to a very light horp .+utkqb5nc,z lskw -7),u qkizontal 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. Iuqlp ,q.c,kuk)t+7ns- w b5kzf 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 used a “glider” (mass of 980 kg 8g m(a5y)-bt 7ede)5b 4kfhga* zxtnuincluding pilot) that was laun 5kteauh7t ezxb8f nd ga *gym(-45))bched 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-stoygdb8i8b br -4ry window 16.0 m abi8 -byr bgdb84ove?    s

  If a car generates 18 hp when traveling at a ste , wvq2d*: y8eyeoo-yqagq ))wady 88km/h what must be the average force exerted on the car due to friction and air resistance?,*yq)8 dy eoqw eqwo2:)g-vya    N

  A 1400-kg sports car accelerates from rest to 9-viodm zfz,:qvf:01 g 5km/h in 7.4 s. What is the average power delivered by the en-v1 ovf z0 fz:qi:d,gmgine?$\approx$    hp

  (a) Show that one British horsepower5s)5chsvrndy:sp 552 nenfu 4$ \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 2txli(-rl rn*zh 4cj+z4c 8f rthe 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 n3z4cras/3x)oqvnc s(y jfb-5 *v yq0in about 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 constant 75km/5bjvo 0c()*4cvyrfyss3 a/-qxnz q n3h.    hp

  How much work can a 3.0-hp motor do in 1.0 h? w5s9kp l-8wu kd8ak6s$a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m gjpmuoz4 /3r)yg6 o8y/s If this motion takes 1.5 s, what average power was developed?4y pgog rou) y/8mzj36$\approx$    W

  A pump is to lift 18.0 kg of water per minute thro3e /wf/mghnm5 3(tq7 nj,ewg ujm,j e0ugh a height of 3.60 m. What output rating (watts) should the e,mm,tweg75jn3 he q/mj0uf3/ j gwn (pump motor have?    W

  During a workout, theqhz2) 7aa(3 rkd sci.r football players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long asd(a 2.q37ih)rz acr knd 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 a 6. 7c-lk7+x 71nctbdcqq 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 t8o)m du f7xp2power output of 120 hp. How steep a hill can it climb at a c oxu2 7)f8mtdponstant speed of 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 310azgmunp0(9a3*y*2 bfec eqem c9(x( p-kg box along a level flg2 uee (z**(e03xnf9aq9c pmyc(b mapoor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts do6h+ txnboxy 3fv a g237dyji 5jk0t7o5wn a 7.0 $^{\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(n ;b 45f wdtkh*rq qkgmuo3i7y.r 5;,u8km/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 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, assu5 7nw;r.y5;trof ghq kqmdu,b4* k3 iuming 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 4tgm0u j(c oz:the first shelf is 10.0 cm off the ground, and the remaining 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 ofc0:z t(4jgomu 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) i fv0e/h1varl0 r tcg59ene).ee4;po in the 1936 Olympics shows that his cent.94 le ghe otnce rp0vr015efeva;/ )ier 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 traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shown in F tba3 f8mpia)dvj;y1 3l il7m8ig. 6–39 is to remain on the track at all times, even at flmaiptid 7m vj8)yb 3l3;a81the 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 aic7fpl5v b:bkpgk)/+j.ep: p agj9p/k rcraft without his parachute opening. He landed in a snowbank, creating a cra pka.p bgpg 7j:k /:/9pce+f5vj) pkblter 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 a horizontal cord of lengthrr,0q- l6kgtz h-kw2w i 8*dda lu29fm L whose other end is fixed (Fig. 6–43)h82z60 fddtqkl g*a--w9u2rwilmrk ,.
(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 p 6:dy 8eefz/kto the top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an 6zfe 8:dyk/epelevation 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 a 920-kg elevator is 28 m above a6t/kqx 19k bjy 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 Calif, hwv xrl sxdk0-+w 4icu0;z8jornia claims that its lifts can move 47,000 people per hour. If thw +xrl0s0u;ci dkhzvw8j-4, xe average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a d aj, dhb754oiogj5ba .i6d)vmam at the rate of 650kg/s and falls vertically 81 m before striking 4b o jvohdima .ig,d7a55 b)6jthe 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 cohawes4hg/ 6; ;,b rcb5z4w pulaster with 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 lasblwhh;e4 c/ u r;wg 6b,p5z4oop 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 int8kcgd,*la z 0ukft8/ yo work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=10 gfz k8c8ta0*k,uld/y00kJ)    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 o(aqf ecg1 hbc. 6o2m7uf 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 /gxesqhu9mkw 5w4)9huqd cd ; zzxji 66z4 u.9compresses 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, whamehzqhx /)wu6qzk6 4dw iju54.xs 9 czd;gu99t does the scale read at its peak?    N

  A 65-kg student runs at 5 fja*ghb;*dnnb g..y3m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope3gh ;fnbn. .b yaj**gd 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 vertical04(q 9(.r+pn kvy;bvy xyfowm distance of 5.0 m in 9.0 s. What minimum power output was usembnpvyvy 4; k9+forwqy(0(x.d to accomplish this feat?    W

  Some electric-power companies use water to store enero09grj mu.fma8 c2prqkp.g2 .gy. Water is pumped by reversibo82pmc.qg. mg.u rfkp0j9r 2ale turbine pumps from a low to a high reservoir. To store the 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 pqsqykd 0 *eoo)j-77uhalf. What is the spring stiffness constant for each of the two resulting sprp)-k *e dqu77o ojys0qings?   k

  A 6.0-kg block is pushed 8.0 m up a ro2:; ;1nrrjul1 rbgscyn:rc4x:1l(mo n w jwm-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 pdyw wysz; epi 0 :n7;.v*zsh6 owm5p: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 t:hd p0y i;s*pw.;np:6v yz s57zwmowehe same, and neglect frictional losses.    s

  In a common test for cardiacce *m)(u(o ife:7bcnm function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estime:c7e fi( (b c*omunm)ate the power required from a 75-kg patient 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 spe7ibi; z:qme 3:nm8nbmws a 500-kg rock vertically upward a distance of 500 m, what wm;:3 bqe bn in:8mizm7as its velocity when 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 rate of)*fh 1cn4as *d:x*fezxct + kc 95kg/s (a) If this water wheel is set up to provide electricity output, what is its fz+*kcte :fcds n 1)xac*x4 h*maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s