In what ways is the word “work” as used in everyda*rntmo* n*6ecy language the same as that defined in phy** r*enc6tomn sics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an odk sdubn( -1/bbject? Explain.

Can the normal force on an oo+* zjnff5op r9x+ybf m mg:04bject ever do work? Explain.

A woman swimming upstream is not movif7 l0no4eu1nj ng with respect to the shore. Is she doing any workne lun740foj 1? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint:b :k .; l +hqmm111zjnxzd.ohf Consider what happens to the dishes when you pull a tablecloth out f mxjqz+ f;zh.o:b.11lkh1mdn rom under them.]

Why is it tiring to push hard againjs,:d-jq ,2cz4 jax pest a solid wall even though you are doing no 2,pa jxcdsqjj4,:z e- work?

You have two springs thaq(v ) lh0h ewpi54yim0t are identical except that spring l is stiffer than sprv wl5mihye0p() qi0 4hing 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 horizo/ ct 1+9lluscvz8zxd- ntal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts dll9c +/-8tz uscz vx1from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potentidnz987yeubsorzg.5+0x 36 z -wegiq; le,dplal energy change when you jump as high az;e-ld+ 7y5,8l3ozbz gwdqs.x ue 6 0ge pnri9s you can?

In Fig. 6–31, water balloons are tossed from the roof ofgy z4tmo +o-bf. 6/lhl a building, all with the same speed but with different launch angles. Which one haz 6+ .y4mt-h ofo/glbls the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point t 0n9hkyw(-ep0lk t2x phat is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle p0pk tw hln9exk20(-y from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you comproqbk f:g: s-qm13:gkd ess the spring by pressing down with your hand and then release it, cfq:qbk1mg ds: :3 ok-gan the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a szzz;woqaq3(r h (3;wtteel wire (Fig. 6–33). The instructor pulls the ball back and stands against ;qzo3 3hwz rq(zw a(;tthe 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 gravitational potential ener exjpz ueoji0: vsm-r0(k98 .lgy when water at the top of a waterfall falls to the pool b mj0oex-erj8(z p. i0 lsu9k:velow?

Describe the energy transformations whenthh,us.r tf9l;3ci y. a child hops around on a pogo stick.

Describe the energy transformations that take place when k f f)i9tfd9e* z9 iqq,0:q5tabuf2hd a skier starts skiing dow 25bdduq9i9itk*qe ,)0 f 9:aqh zftffn a hill, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill oau7 a rd,)lki/3dpz0 pf height h anddd7a pkp, /a0u3r)il z slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log. 1l:* cvuaknk in their path rather than stepping on top and jumping down on the other sidecak1un:lv.k * . Explain.

Two identical arrows, one with tw;th10l am9 m 0ffad.zy/ag u,sice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional forceaz1d 0mm0t,u.9fy f;al h/ gsa on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energ/o uocnf) p3 vo+9 u+;fxe3anxy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfaop+;/+fx39vencuxuan f )o3other clock has to be wound up.

When a “superball” is dropped, can it rebound 8c uu(t.q:*zzjqea , bto a height greater than its origiq*.c(ez bqa8zu :tu,jnal height? Explain.

Suppose you lift a suitcase from the floor to a ; pknk, v0)bm 0rt;otickc pjpp-5h ;6table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the km0 th6- ;)pjk0ppi ;pr,kvn ctb c;o5time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power need 58i0ha nqrw8xu;h.vked rather than the work.

Why is it easier to climb a mounta-py 4 k)vd3swuin via a zigzag trail than to climb straight u v4duypw3k-s )p?

Recall from Chapter 4, Example 4–14, that you can use a p 7 1,vykq ;8.it wyorsrv9pr8sulley 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 qiyk8y9 st;w7 r v1rv o.8r,spmust be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a xd wu sh1h;vnn 7,ragh:s(22z1 y1k )vywzbq)265-kg pile driver falls 2k)nuv7 n2,y(zqhw21zs; )dbyrw1a: g hhs1v x.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work is j30/oythw;go ij/gi06 (g :j5pf5ug d,wksh qreqow t /j0uw5 hji 03ggyqf(dsiojk6/:p;h ,g g5uired?    J

  A 1300-N crate rests on the floo( m6x6smlly3 rr. How much work is required to move it at constant speed (a) 4.0 m along the floor against a f s(3ml 6xymr6lriction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did t :dr: fks:a t(v9m /lj(7qetkuhe movers do (horizontally) pushing a 160-kg crate 10.3 m d vu:kmsk(:tf/qjt 7e(: ra9l across 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 f1d92b1) pzi4 y gszwbior 7.0 s. Fin 1b) yid9s2wzp4z1bgi d the net work done on the box.   J

  Eight books, each 4.3 +g* 4g dsm8 t-a(+irnzyg/mjtcm thick with mass 1.7 kg, lie flat on a table. How much work is requirs-d 8ma+mn tg+4gigz/y tj (r*ed to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can bst;(ti *wt+.oy +doi ce used to liff objects we might not otho.dtist +yi(c+ to* ;werwise be able 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 from accelerating by as.h 27he-hgz a man who is pushing back on h2.ge hh -s7azit parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give aw/o c4ztl)w .lh- aymwr*; n .91dvpvs helicopter of mass M an acceleration of 0.101;a..w-vpvo4)lnd zy*/r wt9ch l wsm 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,a, v8qij(h kj vp5(xc distance 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, varies as/.x4hc/3irkoycxn *ls 5azbmb-f2 j5 shown in Fig. 6–37. Determine the work done by this force to move the object (a) ffm b2r.an-ox x54jz *ky5b clsi3h /c/rom 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 a 4ig 663unb+ ip(. rwfrqv 15ogjhkhp;cts 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 mo)n h+lj d 9c move-cu.2:x.eu*by drq(lecule, 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 factor has its0t e1g6fd3; py6g s6afq dlu1l speed 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)kv t-ee xy:,ch bc772; w8iya 7bs+xesafmp + electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar traveling at 105kmugl +k;j1x 0 h9/ejvdh/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts apr 0izi a r6e(oo3qj+liw83 9ln average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves jew6poq8zr 0(ili irl3a9 o3+the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25-*ps/i;k :q22 mwugh p-z.g7f ss6sm e c5jyki cm when the ball is caught. What was the average force exerted by the ball on th-mqm sz7p 5 fcu/2ke*-s :jy2gig k;ws6 p.hsie glove?    N

If the speed of a car is increased by 50%, by what factor wi.),arl*i( jw30uwzlqx xba0qll its minimum braking distance be increasedzaquw00(i) 3j*wx bqrx,.l la, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level r9vj2g p+ blsr9oad, 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 2sb9p j9+v lgrslammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kgfn /t a:f2- k,9+x:wvn/mukulbh: drr is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if tl-uk2k+n:wnxfm ar dr 9:t //hv bfu,:he distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up b xe*ed,kx 24x9-gaoymw(k lv4y someone who does 80.0 J of work on it? Nl24 vd(e4xx w-g9o,*kkymx aeeglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically wits,oanj z 3wc73h an acceleration by a single cable. Determine w7co3j, sn az3
(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, k, of 440N/m How much mus6 d5zo ucunj+)t this spring be stretched to store 25 J of potential energy? o6dunjz+c) 5u    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is wxs fk 3)ap2og ytom (67)l) x+lwy0nfthe change in potential el7)(t yw) ynxp0ow+)ak o3fsfmg6x l2nergy?    J

  By how much does the gravitational potentx )un6*1 z-(cy+zsvnqo 6ziclial energy of a 64-kg pole vaulter change if his center of mass rises abol*yv6)xno( c+znzu1c6q i-s zut 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h when it stx)r:h.s8cru 04 up2l h2sezxzrikes a horizontal ur p4:82zxzhcss rhl.)u20xecoiled 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 boodx1 q)3d h.8ra j 0:vt); pibkxwk)utnk from the ground so it is 2.20 m above the ground. What is the potential energy of the book retd8dkn:wk). jb1x tau)q;0)vphir3xlative 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 elevatio/b: fb.hlanos1 ld 4v8fw2tij ,o3b8ln of 1600 m and climbs to the top of a 3300-m p8d4 al,2.fjfs: 1blno/3bw o8hvlibt eak.
(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 jl l (l+,eorq6the 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 sp jo,+q rel(ll6ring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5y;b;cd m,(l y9se:b rv.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can ;mve:9bybsdr ; ,c(yl she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides dow*hk3-wah.o .kbsuxz5pvqu0 5n 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 frictif zl 4 ej(gm2-ry2.xyz-kdr4-1 mmmyuonless 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 transformevn90px vczy3v g+*f9z d into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave t 3nf cz9 *xg+yvzpv0v9he ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vci8j92 lczyu 6ertically upward from the top of a platform with a speed of 5.0 m/i6cljy c 8zu29s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness constant is lcbv(;ca42 -3+l8mg 44kdajuo ns mhp950N/m is attached to a table and is compressed down 0.150 m. (a) What upwardj3bo 4s4nmkah-d2v+ m(ulag4 l8;pcc 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 i5chcs od07c fy7k; +htdb12bnf r64dtrack shown in Fig. 6–39. If the block is to remain on the track, even acfd d4bf; ki+5ct107ycr n6dh 2hosb7t the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffcg7g e75koog .6 y*exdness constant k), Fig. 6– eg 6*og7k o5y7xdeg.c40. 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 bejfc ;q+y 5rc2t8+(ef tkz o.yridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the sptyjceckrqe2f5 (8z++fty o ;.ring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to poinzvck(a0 ( xiej 3 h)9k; b,::qganekdht 1 where it is released from rest. Assuming no frictioni(a0gjhnx9ekc kdz )(3 k:b:eqva ,;h, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a sp ou- (oi.p0pvceed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bothi;*. hxu;v sptom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the sprin;hx i su*vph;.g stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a dxuazl1.93 vfdxy* er*ai3q8 nl3 sc.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 z,p ga9:huxd 38os0 svtraveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this ca08zg sohdv : 9,3pxsuollision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reacmyjmi,1)e 7 u 8lcb is3g9(irehes the bottom with a speed of 2.2m/s How much thermal energy due to fri7ijucim (ys g1bi )re 9e8lm3,ction was generated in this process?    J

  A ski starts from rest andop-)iyxqr6 9j7.dre b 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 drop e52dn5xl ujq 1 y3xkktplh8/+ped from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounc8bk:c9g 9p cates back to a height of 1.5 m. k8 cc:9ba p9gt
(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, starti;v5 cx7luyjf 0ng from rest, is pulled across a floor with a constant horizontal fv ;yl0 ucjx75force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of If thekr 9sq y(znmt 0;l)2rz average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The s0r rzl ;)z2(tm9qkyndistance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady ke5j)f9ex v-pa r *c+jupward 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 gdr6ch lj- +pj3gbeb4 b7d q:0light 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 bbq 3c40jdgb:-7dgeplh r+ j6 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 qcl5w(mjcf h7/ladwxaj)l434 p *5gzfirmly attached to a very light horizontal spring, Fig. 6–40. The block can slide along a table wher7dwg a5mlc pwj(x354)czjq*4 hfla/l e 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 first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980v- jnztntuocy*+pvu.5ptil1*;nf(e0 g f -5o kg including p.1tpp n5u+u 0 i5*nvlvy;f-( t-co fjezo*ntgilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have 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 toajc phv9b 9/ v2omaj(;7o0qjc lift a 315-kg piano to a sixth-story window 16.0 ;0p2/(mv o7o ba qhjjj99ccav m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the anlxf+,:j :ppmverage force exerted on the car due to friction and air resistan +fpnxmjl:p: ,ce?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the 6z v hyw1top+ph m5)7yaverage power delivered +m 6howp 71y) hptvzy5by the engine?$\approx$    hp

  (a) Show that one British horsepowe u:v fw4ips lb:1p7fx(ko /o lb hte:30qi8yl(r$ \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 arebz 9d -ppj8 6vv0fpq)g often expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slo q ba:lbtr6y/-r9n8;)gt 3dbi :au dquws down from to 65km/h in about 6.0 s on the level when it is in neutral. Ab6dqr9ug tabqut ar-/:i3) nb8dly:;pproximately 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.gavbi3e w5yt290a4q;xtd k p 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelero+5ag ;f6lin gates a 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what average power was developed? ln+f gg;i5ao6$\approx$    W

  A pump is to lift 18.0 kg of water per min4,- dbchz 2akqute through a height of 3.60 m. What output rating (watts) should the pump motor havekhbdq2-4 a cz,?    W

  During a workout, the football players at State U. ran up the stadium stairs i6gy/ ;2l.0nttdrs v- gr0oj 7o7bm laan 66 s. Th7ag.6al7gt o0os ry;0 jd2rl-m/ bt vne stairs are 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cycli0b7zgy5 dg: - zcky3vdst climb a 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 of 120 hp. How steep a ajsa(1a3, *wvdvw 21fskr- yahill can it climb at a constant speed of 75km/h if the frictional forces add up to 650 wk 3as ydwj*1rvsa,a -vf( 21aN?    $^{\circ} $

  What minimum horsepower must a motor have to be able tooa4uhbk15 6hu:w hd1a(l4 yaj drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of fri4ja h b(4u 1whahaduk:y165l oction is 0.45?    hp

  A bicyclist coasts do-:k/gjg3xpn5w f/ bk own 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(8km/h) buk -r):ro+llgf cn v6+xmpers” 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 thv r+l6:kgon+xcrl-)f e 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 h(brla9n;/ wjoff 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 of 21 cm, and an average shelf holds 25 bookr9(nhwj/ la b;s, 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 193/e tm dwd*eet+ 8lv rbbzz8:+/6 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimumbbtd8 rv: *ez mle/z/de 8w++t 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 alb*rdnp(g9 :v 3l,bih qong the looped track shown in Fig. 6–39 is to rq , pr:nih3gd9l*b (vbemain 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 aircraft withoe 9-. su/j- yp/yrzs modr)e5ehj oa((ut his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived widm(h9.s yjpur( 5 j)zy--eas/o/o ee rth 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 ofln n )*vbbxh. a,yf/4u length L whose other end is fixed (Fig.nlyb/)4 hfu,avn. b x* 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mo.d0tzx o. kz)3cp(puya8 f4b funtain. The climb is made in 5.0 h starting at an elevation of 2300 m. Calculate t8p. dxz c p3fu40.)oak fb(yz
(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 elevator2, s 6 uh9vh4mxlkzus0 is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 47,000 peo 3(9d2tr9z y(j bvlnkw)(rjo bple pern z(9t r((yo 2lrbk jj3)dvwb9 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 ;nrbkkgaodvi,4 )( nl 56bv+h81 m before striking the turbine blade+k lv hn)5g oibd ,4;nbvra(k6s. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. 6–44), the 9(r8i nl r0-zxd t7-v+unax d8)oo/yungg 7qa difference in your apparen0tra7 gx79qa -n)uo/i d-or 8 z nlxyvud+8gn(t 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 cam h; p(t7qck4 i+njk-mndy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1000kJ) m- kq7imknt 4p+(chj;   m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle of 45.mfxe9 4*i(nj9.+vjq 8)tp)sugn vqw f ubwz:,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 bathrw*:hb9-5bdkgb1(l vl z 3j lswoom scale, the spring inside the scale compresses 0.60 mm, and it :5bw*h9 vwjl( 1bkl 3ds-bz gltells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out ovwobq*l 6ck+r3 ij 5zu7er a lake (Fig. 6–45). He release+uqz 3c6kw7b*lrj5 ios 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 climbsfkz5f4j3q zx: a vertical distance of 5.0 m in 9.0 s. What minimum power output was usefj3qf 4:5zkxzd to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped by r)xe4nq93uka6ub+ mn in 9m,,v8 xvqfoeversible turbine pumps from a low to a high reservoir. T)9vkn8xq n 9a34fumn ovex6iqmb, +,uo 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 half. Whf m; 9qk9vdc8lat is the spring stiffness constanvqcl 9 f8d;9kmt for each of the two resulting springs?   k

  A 6.0-kg block is pus9yam*n)l/vkoz*h- n ched 8.0 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 in 3.2 s, how long w rniro057;pgvy 6tb +qp; ihi1r69 gccill it take to accelerate from 55km/h to 75km/h Assume the power s;qhn6oi+pc1yrb7r0 pg 9;i5t rvig6ctays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walk0:susdoq0 airc-f*zel)y m 5. s on an inclined treadmill )cqus :oa05 zi* msey0rld.f- (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 a 500-kg rock vertically upward ave)tzd*6itt 9 distance of 500 m, what wa6zt9tv * e)tids 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 rat, 1 g bfsviu6qs/:rzn:e of 95kg/s (a) If this water wheel is set up to provide electr :gbq:vnu6f ,1sirs/ zicity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s