In what ways is the word “work” as used in everyday language the same as ti) i yf)tgaz(5hat defined in physics? In what ways is )gf ai (t)zy5iit different? Give examples of both.

Can a centripetal force pdau5pi*wfqn.-j f37 ever do work on an object? Explain.

Can the normal force on as4e; a f)c2ucyn object ever do work? Explain.

A woman swimming upstream is not moving with respect to the j svc+4gw9c8vn6e;eh shore. Is she doing any work? If she stops swimming and merely j g ccevh6we+n98v4;s floats, is work done on her?

Is the work done by kinetic friction forces ) 3xkkez5ghp4+: wugm always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from under kzue35 p:x)km gg+4whthem.]

Why is it tiring to push hard against a solid wall g4v0kj,na.n5 jpwa i3even though you are doing no wk.aji3 gpnwn5j4 0a,vork?

You have two springs that are ilyrjkmw9g sj ;g(uii95732 ci j1ue e0dentical except that spring l is stiffer than spring 2 irs e5(m7 wu9ijk i20jgjuly139egc ;$(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free to s z h9a90ohbf68jyd gn)x3l. hrlide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a distanced h n o9xgfzy9hb0a3h68 )lr.j $d$ 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 pote km( yb: 3nieca nfr2l vr71d/4ho8cw)ntial energy change when youldvo(nkhfrri348):/ b cce y17wn 2ma jump as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a buildi.vv.p1wf xz/6y+j,r n f(e mxdng, all with the same speed but with different launch angles. Which one has the highest speed on impaxy1+m(nvfej/ w. dzx,p.rfv 6ct? Ignore air resistance.

A pendulum is launched from a point te +7r-0drpeo 1vfxqzuwzg(o s,/y .u (hat 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 trajectory0uzy(1(o.r -uer q+zpw7 efxgd,/ovs, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress the sprinfvqv0.f67y3 hddhlw -gd w4:hg by pressing dlhq hf6wg-d74wvd:v h d.y f03own with your 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 the1/2nvo ;ktv jz ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the balvt;o 1v/zjk n2l against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational poten9 6ph9 rylc)ywtial energy when water at the top of a waterfall faplhyy 6c)w9r 9lls to the pool below?

Describe the energy transvpcu h+t tmit( 0i3ti(h f2omh241.l aformations when a child hops around on a pogo stick.

Describe the energy transformatiotr ,58ye55q ojkl2 h-bgvl-a vns that take place when a skier starts skiing down a hill, but after 5-qkr8h a-go ,vvbyl55 l ej2ta 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 of:5tjpb)zxi5v,b tu 7 y height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) j tbp75zy:vuxi5bt ) ,there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen logo 9j2 ez,j.(dsbq he(d in their path rather than stepping on top bqo (j(j2s9, ddehe. zand jumping down on the other side. Explain.

Two identical arrows, one with2rfzn k 6xa t:px+u5xtqcy390 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 than the slower ara3t +rt x02x u 9knypcx65fz:qrow? Explain.

Analyze the motion of a simple swinq-ybxz,ua os + is.kbgs3/7l2jlo v..ging pendulum in terms of energy, (a) ignoring friction, and (b) taking frictqo,-37 g/ ujvs2+.xziy labb .sso.k lion into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greatmo0 c3by a/qo,er than its original heigh,o3/m by qa0oct? Explain.

Suppose you lift a suitcase from the floor to a table. The wo:3anry 7fsu lzju *-l-rk you do on the suitcasz-:*j l-u ays7lf3nr ue depends on which 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 fji.y 1p1;eat79pphy -y,f rhwor the power needed rather than the work.

Why is it easier to climb a mountain via a zigzag jgazisak05: : tjm4k;trail than to climb straight uk 4i g0aas;mjt :5j:zkp?

Recall from Chapter 4, Example 4–14, kwooe4b7grb*0pdr69 d 9vvj 1that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fige 1*4vbgdv bor9jorwd9 60pk7 . 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 by8um rj *9oqxuv5 b)+rq the gravitational force when a 265-kg pile driver falls 2.80 muo5b+vxq9rj)m8* r qu?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much wor u0 iua*fjttm3:.) ,t0qoohqm k is require.himfoo30 :mutt,)q 0tqj*a ud?    J

  A 1300-N crate rests on the floor. How m :khu0ysa3owcb6y qbv*3 y0d0 uch work is required to move it at constant speed (a) 4.0 m along the floor against a friction bqo: wky3 bs60ahv0y0y* c u3dforce of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizont-iwan ol b0o3+un7 gx/ally) pushing a 160-kg crate 10.3 m across a 0-bxaui/l+3 ogwn on 7rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is acceleratexfp+z gg:)d2 xd by a force across a floor at a rate of for 7.0 s. Finp2+fz:xg) gx dd the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg,tkzv2/ ob 2om, r pruw93uv3:t lie flat on a table. How much work is required to stack them one on zub,3rrk v2p93mtu/: wvo2t o top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects wq 37yglmr:j8ohx -.koe might not otherwise be -jqm oo :387gk yxr.hlable 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 kep9e mhkva;n .1u:tylo;o5 z lc7t from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6- 9 lhk7ouoav;em;:zn l.cy1t536). 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 accmq9boiu8u3w4i )vw k8eleration of 0.v)q8umoiw3i wu8b4k9 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 axis is linear an xr -2z:, 12lqbbcoalw)w-a 3aqfzce*d that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shown in Fig. 6–37 m up*x0tm+8hyksj,5 c. Determine the work done by this force to move the object (a) from x=0 m to *uj+0m8s, ty5hxpkcm 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 part ul 0pxotl)s 9bgn8m4;icle 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, with masskij413reas+xecx2,ma 5h hwz, y4n. s 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 speed increased?2 7i0en/gqwo3r7 qfwq $ \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 :u- qxdasx5 oml:.pf:$\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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-ka-d:moorc +5s gcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an aver7sor*(yhu.:y ny) mk fx1q*zeage force of 110 N on the arrow over a distance of 78 cm. What is the speed of thz ykfn1ru. (7o)*m ys:xh *eyqe arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves bnn e7y.f): s39bmlws/.fds pa fielder’s glove backward 25 cm when the ball is caughtw7)dyn s/: bp3 emsn 9.lsf.bf. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor w e+v565 9fkdq5 pofhmdcyg1,3 mk/k hjill its minimum braking distance be ik,/ k56mg9com5ed3fq15kf+ hjhvydp ncreased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene onr(ta-k/7x4xxk lqgyuqp,3y 1 a level 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 es lu-xkyp3 aq x txy(q,4g1k7/rtimated 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 reaf.j 3)khm* v1 zgj0c3bf 6wyk/1puroh ches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resi)um/y .01k3vbp1ffh j hz3 kjcw 6gro*stance during a pitch, if the 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 by someone wt9ssb2r*/z a5ibmn b :ho does 80.0 J of work on imsb *:snzrt59abb2/it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration j*gaq m 3*sb7 k;8qphzby a single cable.h8gbk*7aq3 qmzj* p;s 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, qrund,5p ja15k-lje k eu,wv b-+:r .uk, of 440N/m How much must this spring be stretched-.u,ule rw 5bp: j,r-kajuk+ 5e1qvnd to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 qdad s/ 83 (qndulq jr5 nm*e)9vdk:n1m higher. What is the change in potential energy?*v /j 8un1nlqnd(e qd5m)d k3r9q ad:s    J

  By how much does the gravitational potential energy of a 64-kg pol0*7x2 i *gvy s0uvl jzx)o/ayze vaulter change if his center of mass rises about 4.0 m du*u/0vxo0j ys2 xyz )z7*gvlairing the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h whenkc )vgm7dv5s uk3)e3 z it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constandvuk smg3 3k75z)cv e)t 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 abov 6p5x*bk4,9vlk ztvix e the ground. Whaikbl*v,t 5xzv64kpx 9t is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m an:a2/5yssjvyp d climbs to the top of a 3300-m sjy2v5pys/:apeak.
(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+zo zdqakx*09hnbz5 , is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of th xbqz5h0d *kzan z+o9,e spring line up with the ruler marks?    cm

  Jane, looking for Tarzanc ;7hy4dbq n0g, is running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. 0ygd47cbh nq;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, r8pay.6fkfo,*stwq*qj u.6 g fgap 4 (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 frictionless 28.0bhgac4ektohfxoo*8 f*b ., (4$^{\circ}$ 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 transformed into gge m9m1qlfg (y4 x.)am-ha,yl ravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar e4gym( , hfy-a)m 1llq9.mxga with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the c.sz3;9jj ch/ukbd3a top of a platform with ad.a 9zhks cc/uj3 b;j3 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 wucr6dx(42av:z (okpmass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.1pk6duaow rvx4 :2cz((50 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 da*4vv6o4ettvc d( ;jtrack shown in Fig. 6–39. If the block is to;dtde c46 v(avj 4vto* remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is hwff+iz,44w e+qp g+eb :7d l*vfa:oaattached to the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial displacem,4qf7+: ze4+geflw a :*wvi +bdpofha ent $x_0$ 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 ti19jy( m-ecfxtc9et)a ed to a bungee cord whose unstxcc-ya1(tetj )9 m9feretched 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 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 poin*-ad w:2eyi1fnh6h lwo:r l d3t 1 where it is relea2dnlyr :al*dwe h3 i6-fw1:hosed from rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrvv (x9 i1b byz2kr4cwftyy/-3own with a speed 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 playnj36 xoqs 8 q*:2uu7jnmtxk: ced at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the smqx7j:oyu:*tnkxj3q nu2 8 s6pring, 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 passengers.

  A cyclist intends to cycle up a 7.8shxg;:o2 k)k 38zr crc $^{\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 i ,ubhvxrjnh/q)76e( z n opposite directions, collide head-on and come to7)bj u v6qxz( n,/ehhr rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high 7 2s;galfe-dzand reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generatesg;z 7fdl-2ead in this process?    J

  A ski starts from rest and slit:mor*y v ugxw5w6xc + -da60udes down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 xb-8pa zz9v/fwa1v 7mm 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 of 1.tpvz6dh des mi4:em m858ymd3ut )v,)5 m. pm4eu38)8h 6dz5m ym titm:d,v svd) e
(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 fsx;y b6d ,, dj6mtyk3urom rest, is pulled across a floor with a constant horizontal force of 350 N. For the fiu6x3ykb d, jtdm,s;6yrst 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. 6–416rrvr. s6ki t7 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it rs6r.i6 tr 7rvkeach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches ti1vouk468zam bw 8 dq4he 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 light horizontal 7byvd/c .l (mwl71agpspring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic lvlbw1d.7 my c(a7/pg friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spring, Fig.:f-w-(d. hkn5uqu ;axfh ofu7 6–40. The block can slide along a table where thuw7fh (-hu.nd -ok:a u; q5fxfe 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 980 kg includ;pdf fq kg 91a f-gf4ifg07umy veb0(;ing pilot) th( 0ggkf1v0p;ff ya ;d7mbfg49- efu iqat 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 motorr2.fugwuvlp9.n 1 ak.kmp5ebg n6o2 , to lift a 315-kg piano to a sixth-story window 16.0 m .lnu k ,pugw1k n6gmao25.b2p .v rf9eabove?    s

  If a car generates 18 hp when traveling at a steadqm+ i4morbhi x/7x 4fgy-ki: )y 88km/h what must be the averam7 f4+/ym:)xk4 qg ihoiixr b-ge force exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is t4;gdo2u fn-xj he average power delivef-jxo; g24 dunred by the engine?$\approx$    hp

  (a) Show that one British hortoc zzev3v z4p4)an9/2 e fsl:sepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilowatt-hosg 9pcf.p)m (rf *khfgv7z4a 9urs.”
(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 thaui;o ;zeyo 98xt her 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the c;u9ez x ;y8ooiar traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp 2x4((javxws1x 0tubj motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rert pph*xv5akbj d5-*;st to 14m/s If this motion takes 1.5 s, what *v*5dh px5j k;ar pb-taverage power was developed?$\approx$    W

  A pump is to lift 18.0 kg + :6nrht. om)gm nrk/uof water per minute through a height of 3.60 m. What output rating (watts) should the pht:nn uk og.r+m/)m6r ump motor have?    W

  During a workout, the football players at State U. ran up the stadium stab0 v+)he/ na0 +elxzvssnumf3: 9,xf6akz)vgirs in 66 s. The stzh e k++v 0am0fn)xs x)s9nulebf:3z, avv6/g airs 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 cyclist climb k2u ,rh nu)-zq 9c,h8mclwo8da 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 powee4i amz v8e7o5r output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces add up to 650 N?az4mv5 ee7io8    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg b11y3 zx-wbjvaz 1 h;vr7aax:b-b m8hbox along a le-v jz3vb1;hbbamx8y b:z- 1awxa1h7r vel floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7cs+ ro4dy k80z.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) bumpdce 0p5fq jbz*,2nqw7 ers” 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 t qdq*jnpb z 20fe5cw7,hat point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the groundb (5gypxwy8: kq; dg0:caqtn, , 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,t( k;yqbp gw8 :a0cxg:n,5ydq 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 j4; (ttz;sqqm (Fig. 6–42) in the 1936 Olympics shows that his center o;;sq(zq4 mt tjf 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 with7iqr16).hb hu. dxgrja9j/mr out friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop gdub ahrxrrj j6/ih .m )7.91qof 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 31b;g*jcl0iaq iyd7*0y1nnra70 m after jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.q 7iiy1;n*y j*rg0 0laba 1cdn1 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 horizon:omz:l/ gczv83c/r5o( h)w e-ag1rxo k 4olcatal cord of length L whose other end is fixed (Figcvwooz: mga: (r-l)l43xo8z/5 1gck h ro eac/. 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 s1s0zzm3d s8y 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Calculatzys0 8m3szs1 de
(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 abodpe(ylmz)58k s )j,qa oib41eve 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 c7-mz izpr8 k*47,000 people 7mzzcpk8r*i -per 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 aft) ,hyh- j,2tclwi7a nd falls vertically 81 m before striking the turbine blades. Calhat7-, t wfcij,2h l)yculate
(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 (wnkiu(re*c9 2 Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weighe9 ( n*rcukw2it. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into wqqvtjpm;0 +i(/7vs vmork, how high could an 82-k+j7 vvv; m0q/(mtisp qg man climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an uhuwc e)3 0a+t0v r94dfdfyaf9pward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale nv: 8c ijdj*/he :6i px4yuku9compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak uj*k/nv 6j c:pyihd iu4x8e:9?    N

  A 65-kg student runs at :5voal9 km(hj5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his velocityv:j 5(m ohlk9a 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 vertivcc )wu*k.cy, cal distance of 5.0 m in 9.0 s. What minimum power outputcky,u)c .wvc* was used to accomplish this feat?    W

  Some electric-power companies use water to store0 zw c)ab ;rfudur,dv3cpez-o+ch 8 82 energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy producevdhb duoc ) z8c8; pcr03aefu,2+ wzr-d 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. What is thevy1 arpu )un(+ spring stiffness constant for each of the a1y)+ ru(nup vtwo resulting springs?   k

  A 6.0-kg block is pu if nbaua 5lpq/vz5bn2(s 7:vx9q+ x6fshed 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 3.2j- hcglz. n0* wf4ocn. s, how long will it take to accelerate frfc.o.-nh*jl4cg 0w znom 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), t;diberv b+ u:0he patient walks on an inclined treadmil :ibue d+vb0r;l (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 a distance of 50lhcx4 c+f:j)bld+ 1)1jtyv gx0 m, what was its velocity when it left the volcano? d:xhlv)+x cgj+ 1 f14)lcbty j$\approx$    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 95otr41d ld h(k l0f4uv4kg/s (a) If this water wher1tfho (4k d0 v4ld4ulel 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