In what ways is the word “work” as used in everyday language the samey- zinex7gwt+v0phww*;d 3si7e5 zeawl9d17 as that defined in physics? In what ways is it different? Give examples of both.+n di t7w vw1w5y ep7ag07s zedh9i*xel;3zw-

Can a centripetal force ever do work on an object? *ek ak4 xtm32uExplain.

Can the normal force on an obje9 l40een+k kmdqrv/4w ceps.,ct ever do work? Explain.

A woman swimming upstream is not moving with re ht+ c nodwh nv/(o0u1rza4z3 e) ay*kd6.sve4spect to the shore. Is she doing any work? If she stops swimming and md*vnv3 oe1hda0 +)4sr z kuzny6awc/.(eht o4erely floats, is work done on her?

Is the work done by kinetic frictiong5 -h wkxoyr,r18)uk 0w-j myt forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from under them.t10rkx8-r-hj5g wyuk )m ,ywo]

Why is it tiring to push hard against arfp od44cf(6beytn-nzv / tvty 1vh3pap -6.0 solid wall even though you are doing no workyc (16b.-v pfnthp oa/v0dp4ty zve-t nf34r6?

You have two springs that are identiuo9lcah )tb4n r.m ;c22el,oacal except that spring l is stiffer than spring 2 e,ch9.lmb ct;ar2ln4u )ao2o$(k_1>k_2).$ 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 constant3ky3rgxa1/9 (ycw v vp horizontal force on a block that is free to slide on a fr /kr(wcp1vy3g93v a yxictionless 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 ip w;r7w u)3g1m 4wlnfw 1tk2dgravitational potential energy change when yu4n) 2pi7l1ww3wd kt1 w;m grfou jump as high as you can?

In Fig. 6–31, water balloons are tossed from the roof(0t*tucv9nqghtlk9d0 t cl z.g s;*4t of a building, all with the same speed but with different launch angles. Which one has the highest spedtv; z*9th g ut tg9.*qkcs04tll0c(ned on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowestb0ttar1 b6,ks point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the sec br 1ktt60b,saond 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 +kxd y+ /a;b jkfjg9yfk:ks)4upright 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 consekkx fd/y 9:;+)g4 jyfk bj+ksarvation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). Th3mq m.-)wsqr 5ezj046yvgzd jlix+j 9e instructor pulx zy -ldjz54 6j.+3vji9mgsw)mre0q qls 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 pushing it. Why?

What happens to the gravita-sl,0c 7cyp.dv8ie bctional potential energy when water at the top of a waterfall fallsvibsy. c d0l8p, e-c7c to the pool below?

Describe the energy transformations when a chgmjgl g08s uq96kufs ur8a) e +:h41kdild hops around on a pogo stick.

Describe the energy transformations that take place when a skier starts skiing-n 8whseh2 y4*b jzn7o down a hill, but after a time is brought to rest by*seh47h -28nyo bn jzw striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hil(itwawa wr6/k4 2 /sscl of height h and slides down. Does the velocity at the botto( it6/aa/2 swwwc k4rsm depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer w2 xnp-q hue4+to step over a fallen log in their path rather than stepping on top and jumping down on the other side. xwe +2u-4nhqpExplain.

Two identical arrows, one witr-aw1 +9jz.rxr/ x uxh9lfw;;;z my bch twice the speed 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 penetrate how much farther t -y.xxlf ;1z9cj rm9;z/ruhwwx+ a;rbhan the slower arrow? Explain.

Analyze the motion of a simple switxorg 2cva,0,nging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Expl,x0va2 o gt,rcain why a grandfather clock has to be wound up.

When a “superball” is dropped, canok52iku rj* a9 it rebound to a height greater than its original height9i ja2k ou5kr*? Explain.

Suppose you lift a suitcase from the floor to a tapkpq+i.3hm.ogd 6e a3ble. The work you do on the suitcase depends on which of the following: (a) whether you lifte 6d opg3ka.hm.qp3+i 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 p i vgwas)5:xy8(2ry;d m3evrh ower needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to cli-9apf r*d9x cwpqwqhav l,+:.mb straight up?- qh*: p.f9clw,w+vpad aqr9x

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to de/a*0gerhgob) d2ay m3 crease the force needed to raise a /hrad m 2*0eog)bagy 3heavy 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( xzi.uxo14q-.i nyui ft9e5o when a 265-kg pile driver falls 4u n(. zxo 15 9iixo.u-teiyfq2.80 m?    J

  A 65.0-kg firefighter climbs a flight of sta9 xmpk5adjn+ jxkrzq:i9 5 83pirs 20.0 m high. How much work is requirk xpj9zr+pqdami59nj83x: k5 ed?    J

  A 1300-N crate rests on the floor. c.v* go2bgta 5How much work is required to move it at constant speed (a) 4.0 m alongavb*c5tog2 . g the floor against 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 ae,)iczpo0dkbdn o/e (l-( b3 10.3 m acrosk ( dcz-0apb)b do,(el3 enio/s a rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate of ku8 h2/f6 f2rogrn9 er for 7.0 s. Find the net work done on the 9f2r6une8orr2f g k/h box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a tacnx c3o3 b c;qjnvs 4,zn/8h3cble. How much work is required to stack them one on top of another ,c sj3zc;nv8coq b cn3hn43x/?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects e2,:zrde4v e8pv gi3mwe might not otherwise be able to liff. Show that the ratio of output force, : z 8m3vrg,epd eie4v2$F_{\mathrm{O}}$, 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 38gq hu;8x z m2m6gs3ro.6 m down a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coeszg 8r2 hgu3;xqm8m 6officient 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 helyiagh2r 0+touv2)da 3m/6i(k 3q:zuipu 6v mjicopter of mass M an acceleration of 0.10 ghag+2am3uqyoup3 ):0div 6 v2i6 zuj /rktmi( 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 dk2acs7)3gw*zau :e im istance 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, j5 depn+ 2cgpvnh vbah7+u(6, acting along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to m+vha2dcnnpj (e,5 7h+ bpgvu6ove 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 o7rq *zb dgu)q2n a 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 molecule, withdn.,.u 5mbizq 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 factor has its sps4o*ow6qy+ ,stux l2a eed 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 ele(trqr;c7zx (hwn5 : pzctron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 105km/2unppl3,qh +zh?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow v5-+ tchq7hlz ou).lowhose string exerts an average force of 110 N on ou+ h) h5olq.z l7cvt-the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backf q)5j 8odhh- -brammsuk7v r+8o9i- rward 25 cm when the ball is caught. What was the average forjfi h8 oaq s-rv+9mu7m-ohr-r kb5)d 8ce exerted by the ball on the glove?    N

If the speed of a car is incrc k 8nt-b+-pfbk4jzt) v/kb;v eased by 50%, by what factor will its minimum braking distance be increased, assum; 4v/nk bf+bjbv-z8t)-pkck ting all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a le f.do4 lpc1j uj)5x9nrvel 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 speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not mattd cujx5f1 onpl9).jr4er?)    m/s

  A softball having a mass of 0.25 kg is pitched at By t7qjsz4yy vw:0he 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 distanv:wz y7qsj40y ce between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who does 804;/,y iskni6c w) kx degu*mx )j4+tjq.0 J of work on it? Neglect air resistance. x ju;s4 n+jxk)t ,ygqdei*wc)m64ik /    m

  A 285-kg load is lifted 22.0 m ve9 p zkiz 24yq7kj)zx.mrtically with an acceleration by a single cable. Determine k k.zi7jxpzzq2 94 )ym
(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 stiffnesp ,bejyy e3a1i r9sl30s constant, k, of 440N/m How much must this spring be stretched ts 3ep,il yj1e r9bya03o store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is t, hplvhdhavny6* . d1t2)p 4mvhe changey6 n*ppm2,h)lv4td v.v1hah d in potential energy?    J

  By how much does the gra+w9zbf o).z.ae/5rcwmwus s ,vitational potential energy of a 64-kg pole vaulter change if his center)w,m.zu59wz+sr .owe s fb a/c of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface hagf3uy i */nkfp8 qh2 ;q )dnh-:3hrheus speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness ci dy-*:q) k p/3qeu8hhu ; ffrh3ngn2honstant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the g8rz ns 5/hwlbfm*a.:i round so it is 2.20 m above the ground. What is the potential energy of t/zw n.f*r8 ims5 ablh:he 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 climbs to the to7shy,q 7gevr (p of a 3300-m pe7hs( qrvy,7ge ak.
(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 of the spring fd39 mb em1dj37i;z ukis next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up withm9;ukj 3ez b3m 1fdd7i the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/lrlprb0;-d f6 f1/fqzzz+* jfs) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upz jdlr/ *+fbq-l r1f;0fzfpz 6ward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides dz l6* s.q,0fup.zglbgqo)m1x own 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 28. )f3vlc- +mi((+ydl;mhjwz 6jyphzy*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’sdp 1xuozmn0;kxo20 (* -xuuczmbf p8us)m o-+ kinetic energy is transformed 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 c kzpux-umm10 u+x (s-ooo 0 p8n*zud)xbm2f ;mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward frf */5snukstq v2f k7 :zv;ds(4h;n omub:ktb5om the top of a platform with a speed of 5.05sk vfnob 4ksum75nq*t; h ::vdfb;zuk/2t( s 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 sprinns; q+hd y 3;hndxzh ol+/ddgco7n,70g stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What;d+syd7,+lz o g;xh/hh0cod73n ndnq 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 traci 5m22p:qyy4v2 wm .2kqx jwolk 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 h22p x.vy jki:2q52 4owlqymwm must it be released?    r

A block of mass m is attachwnom..::vg tbr27k6 y,nz qwted to the end of a spring (spring stiffness constant k), Figr,72 g to.n. v6:zwk:nmqy twb. 6–40. 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 jumps from a bridge. She is tied tob sh.275 tx)dm zbvuh, 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, uhb, z .7hxb)s2dvtm5 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 w fh,yfq63 ea lds j;hc,m;h/;1 where it is released from rest. Assuming noa/ ,s;;dyc 3qjhlmwh ;fhf6e , 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 ms+7-bj s il1 ow(-tcki/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 elevator ,0ohepv v*ipd*d d65 vub.b*l+cii4vu h7n x2 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 rest. Let M be the total mass of the elevator and passenpl*vx bvcph*, 6d vdd50i4o2n*7e.i b uiuvh+gers.

  A cyclist intends to cycle up a f qx)baw,or*) 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 95km/h in opposite dnk r d,(y.qte1irections, collide head-on and come to rest.nkde yr,(qt.1 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 and reaches the bottoma7fg rm ;wwa8x;,e1mj with a speed of 2.2m/s How much thermal energy due to friction was gfmxjg1m7 ; w;8aeaw, renerated in this process?    J

  A ski starts from reswy ps kx6,nggk7)z./y 1ol7ybt and slides 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 13.1s sd8lgg- 7z- /gtlqh0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a height o l4k-ug l,h)oif 1.5 m.uio), l-kh4gl
(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 across a floor wt5 ik 7z wt3-mwz7xe3oith a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is7izzt e 75owtw-x3k3m the final speed of the crate?    m/s

  Suppose the roller coaster in Fig/52u,wu +yegiumn3p t. 6–41 passes point 1 with a speed of If the gumn35+t,/ w2 epuy uiaverage 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 reaches the foot of a steady upward 1yiba -c b wv-,*br-b;e8.0 $^{\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 1d ( rj: xbzv(innl+8jy,nji+attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning backn +v iy,1( zj+ 8xbjnrdji(:nl. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very 2fgllqhhmu0 l w40 fp*dy5r7x)o:s.vlight horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibriuhh7 lw2ovdr u.04p f:0l*x)ygqm l5sfm position will it stretch on its first swing?    m

  Early test flights for the spacrn4vig t0 (oim vt5v:j:1m8bz e shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontallyrtv5:48gm bo z:miit1n v0j(v 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 pf (rtx)wfx v7/ 6iiz04wvlk.tiano to a sixth-story window (vf6rl0fxw ./xttz 7 )k4vwi i16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h (8 o05s4n r.ubrcnye twhat must be the average force exerted on the car due to friction and air resista4r8nn 0.ocrb e 5stu(ynce?    N

  A 1400-kg sports car accelerates from rest to 95ksn8( fnu uwm* 1u+3vvym/h in 7.4 s. What is the average power delivered bmfusy+*vv3uw n8n(1 u y the engine?$\approx$    hp

  (a) Show that one British 28jts5ez.oo 3 *y rzhmad :a8dhorsepower$ \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 t; obk0l t 0to;a b+t75zbi,kkuhe 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 c;i0trx )l3uth4ngi0her 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutraliiu tn);x3t 4hg00cl r. Approximately what power (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 dqk- yux l)hm;3h4bu *u il/1x1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from m,+pyn axccn6a r; ;c/rest to 14m/s If this motion takes 1.5 s, what /c;6nc+nam,c;y paxraverage power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. Wvno czco yj4p03/hrrj55n0t 1hat output rating (watts) should the pump motor have? nr ojht5yvn1 /jr03c5p4c0zo   W

  During a workout, the football players at State U. ran up the stadium staii3 ww khm7vp6; 10 .trcd;lxsj l0cgw*rs in 66 s. The stairs are 140 m long 7i t; 0mgpw.kch0;rlcv*lwdxw6s3 j1and 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 6.0 9ypnrjb(2b(n $^{\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 of 120 hp. Howtd)n pql6e+q1 steep a hill can it climb at a constant speed of 75km/h)+n1qdt el6 pq if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to ua 2g)r9auh2m257f3od4erqv bw . xv mdrag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction is 0.4mo23.umg9re v vxdu2qf7abwh r)a4525?    hp

  A bicyclist coasts down a pqg y2prak0l .04r8 hb7.0 $^{\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” :g(t vc7 t mbi0qzw2;qz/t 2fxthat 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 into a sol t;fixg2mtt2vz :b(cq/w0z7q id wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off t:pl,ho ue4 2cn2gkvrv: ifr d64i-e1p he 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 of 21 cm, and an average shelf holds 25 books, i1olrvfeurk4-epv2i cdgp n6 2h4 :,: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’wai1seckx ;587) 4lfo8* gfuh9omcckmy a8 *es famous long jump (Fig. 6–42) in the 1936 Olympics 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 wkklaeam ow o 4*7i8c cyem;)9xcg15 8fuh*s8fas traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m slidi:u bm+ su;tqfl 6j)ozpri hu.h,7u36 ang without friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the ver7 u) :. i6;fo3huu ,rslj6btp+m ahqzuy top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without his parach,e xz8 bh36dc0xbjy-aute opening. He landed in a snowbank, cre-b3ax860hzced , jyxbating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other endti gp8iug95nze7 7csw /y: .qr is fixed (Fig. 6–43).9yqwiienguc7z.ps8 7rt/ 5g:
(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-high mo qw p6v( *kfz 2lc*p8d9tc7cniuntain. The climb is made in 5.0 h s pcp8i792nd fvccqt6z(* k*lwtarting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m abodvtk 3tvoxc)n.cf2 4. szq7*c ve a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move -:bk wl1xraxo7 npf1/fw(b q347,000 people per /banx7(1:fpolbrw-3qx1fw k hour. If the average lift carries 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 vertically 81 m beforemc+5c -7 * 4gzoj 1icaexow+lt striking the turbine blades. Ca 4ao5w+t7ilxj 1 zoge-+mccc*lculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (mzm iuv(rrtrkf6/dex9- 93j3 Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is3df(x-mmir9evr ztrj u36 9k / 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 converta bp v gjx(g-/k(ac2w. a candy bar directly into work, how high could an 82-kg man climb a ladder if he were a gbvxwkag -(p 2c(j/.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 fired at an upward angle of 453e wex(14 -(yi lamxrp.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 bauh *siuvp m8/b4bv q57throom scale, the 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, whb7p5/4usb8qmvu * ivhat does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (Fig. 6d 0jon- n8 hv 9f;r(sp1tywj/k–45). He releasevjjs ;ho0 rk nnf8 p(wd1t-/y9s 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 5.0 m in 9.0lfn0 xhs9f3)xamk ( 1cb0e+al s. What minimum power outputa0+l 3l )amf(nfhxkb s0ec9x1 was used to accomplish this feat?    W

  Some electric-power companies use water tobo7zb9h0 fqcp laum3ojq90*; store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-paqb07 fczh lo990 ;jmqbou*3MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What is the spri mctew/f 8sh-,ng stiffn,w-f/s 8hmcet ess constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m q*.txi, g2v tdu5s1f-oe6e tq 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 fa67hr* hm wl3mrom 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 slrm63mw* h h7atays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”)c cb.7of.vmf 7 j+l8vq, the patient walks on 7f8. blq+vjo 7 .cmfvcan inclined treadmill (Fig. 6–46). Estimate 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 spews ala:g3 3 m*h0k;ibu**m(h fkbo js n3ap 500-kg rock vertically upward a distance of 500 m, what was its velocity when i*30hp ;gbou** b hk3imknf 3ajs aml(:t 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 95kgt l h7( luhzg-*w/x6zr/s (a) If this waterlhw6u-zr hlz(/tx 7 g* wheel is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s