In what ways is the word “work” nn7f kdd)8c5i4 -fgps as used in everyday language the same as that defined in physics? In what ways is it different? Give exad8 g-fi4n5 sncd p)k7fmples of both.

Can a centripetal for-0+xytbr i:w1 j ,vjomce ever do work on an object? Explain.

Can the normal force on an object ik 5kyb /1i4vmever do work? Explain.

A woman swimming upstream 0ywbu/y up xn1s y+hfvw-y;+2 is not moving with respect to the shore. Is she doing any work? If she stops swimming and merely floats,bu0+n1y /syhvy ;+wpy2fx wu- is work done on her?

Is the work done by kinetic friction forces apyre 3e v*3pt(lways negative? [Hint: Consider what happens to the dishes when you puly* e(3ret vpp3l a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall eve614w+7r kwh iab6 a5gp chlt4n.m9bysn though you are doing no work t r+ahwg66clk91hay54.in pbmw7b4 s?

You have two springs that are identicalgj2i;f fvn.7 pa4 j1tx except that spring l is stiffer than spriapv j4nf 7it12g;xfj. ng 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that iszj xvkm,u2j2( free to slide on a frictionless surface (Fig.6-30). The xvj k2m2 (jz,ublock 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 gravitationy /w))8 ifxyj;og v2e-bw*sloal potential energy change when you jump as xjiv)oys*wb8fw-2lo yeg; )/high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a buildid0* vgped hkqf6x6cvcyl ,7b-,sv )t6ng, all with the same speed but with different launch angles. Which one has the highest f)7cqc*lv vvg0- xdbh 6,t6pskd6ye, speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a , ij 2;fx/fepsxf4euc, hi)z9u( yp9xheight 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 thhi9/(fxj p29 pcxe4 iyeu,f,ux )fs;ze largest angle from the equilibrium position? Explain.

A coil spring of mass m rest pjm;s8tr 3kv/s upright on a table. If you compress the spring by pressing down with your hand and then release it, can the sprink;8v3 jt/rpsm g leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33)d texstzh;p(i)+ ew 0sp1 y,6t. The instructor pulls the ball back and stands against the wall with the ball against h 1xs+( 0p6ethpzsy, t;dweti) is nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when *cwjqlqz w*q2i 1enj3;le.b7 water at the top of a waterfall falls to the pool beb3e.;l* qq2q zcljin7w1wej* low?

Describe the energy transformations when a child hops around om 0y;e*yug-og n a pogo stick.

Describe the energy transformations that take place when a skier start s;3j8v-n 5ejz/s kpapc2iv tzg x568h3n +cvbs skiing down a hill, but after a time is brought to rest by strikingv8p - zn53z2+e8jv/is jcka 5h6svctxgbp ;3n a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of heightiz,z/l t5 3ah +b,b hfdm;-9elrrm ,fe h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a)3 fltb m 5,9afd+ bzh,,-/zrihler; em it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather than stepxjpvp01 ;g +mlping on top and jumping down on the other sp;pm+v 0xjgl 1ide. Explain.

Two identical arrows, one with twice the speed of thfny 34+e3p puqt9u+ ace other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetr3pn ay+9tc+4fu 3q upeate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendub/3 b)1w)e3; fi giiew /*nuhsots f0plum in terms of energy, (a) ignoring friction, and (b) taking friction into accounfu/ i/b)wnbo hew)isfe*i30 p1 s3;g tt. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a h/16ra s(uh nsqeight greater than its original heia6r( 1/susq nhght? Explain.

Suppose you lift a suitcase from the floorr9cp) i4igom x36f f)j to a table. 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 time it takes, (c) the height of the table, and (d) the wfpg6xf94 jmo))ci3i r eight of the suitcase?

Repeat Question 22 for the power nee8yk5v 112vgx8x ;qigz zqxa,sded rather than the work.

Why is it easier to climb a mount;c 8:kqtn c,hiain via a zigzag trail than to climb straight u; :kc,cq8nt hip?

Recall from Chapter 4, Example 4–14, that you can kqr- 6le:q:czuse a pulley and ropes to decrease the force needed to raise a hlzeq:qr6 c-: keavy 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 1lh h1ptf 40-ptlk.zpthe gravitational force when a 265-kg pile driver falls 2.p0phf-t.zh1tl p kl1 480 m?    J

  A 65.0-kg firefighter climbs a flight of stairsws :b-(lhuof. ws1p (h 20.0 m high. How much work is requir(u oh s:hws.p1wlb -(fed?    J

  A 1300-N crate rests on the floor. How much work is required to move it at c 9glxlj7nkg2gpsk+0 f:.kj 6 bonstant speed (a) 4.0 m along the floor against a frictij0kgg l7j .glx kpb9nkf:+2s6 on force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing rfd5s : dd;+7gup uthe8 *tj8fa 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction wasfduh*:f +ud8 t8pjtr 5sge7; d 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor atvb +m:f7 m xkcqkgt*() a rate of for 7.0 s. Find the net work done on the bo(+fvgqxtcb7 :m) k*mk x.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg yrt )wyme+,d*, lie flat on a table. How much work is required to stack tyyrtm,d e)* +whem one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to l1x. z0/m u ssjc-cujin:w;2 isiff objects we might not otherwise be abj wc:c sunz j-1ximu;ssi20 /.le 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 slide1aewr np :cfna83v r8j64q/vo s 3.6 m down a 28° incline and is kept from accelerating by a man who is pushing back on it prf:8wv3v ej/q4ra noc1 npa8 6arallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M an acceleration o kl5s :ou;r8glf 0.10 5r :s;ugllk8og 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 x.n y. t(0gqvsbyj+8 h1q7ehz f,cz6qlinear 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 a-zcc34: bnmb7om(j t5 g;xr iaup 9jd6long the x axis, varies as shown in Fig. 6–37. Determine the work done b4g : ibzr7-mu5;bjj6xop 39d(cac mnty this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted o c1907 y98ca o/7jnmgomankxtn 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, au7ew;v 1oscvej3v 9vb:8x 6 kyn oxygen molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow ci:h2k-8hf r)dd-ll iis doubled, by what factor has its 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 a 6aoq7bgl)(u mx-g w-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 as, fp;ez*6f bit 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average cog)7-w+ tpu)tc:a ucforce of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as p c+ c)c)au7ttgow-:uit leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove bnlgxw2 l- -mcm *r,xt*a++hn:oxx,nq ackward 25 cm when the ball is caught. What was the average force exerted by the ball onlxm: x--n 2haml *+,o g,nx *xw+tcrqn the glove?    N

If the speed of a car is increased by 50%, ob y7532ihtf gad(sdep5p*5(ijuc9i by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore th79t (ddo5iifepycu bjp a* 535 s(2ihge driver’s reaction time.

  At an accident scene on a level road, investigators measdj4 pcyg4n- 8(rs:pi xure 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 tc-xj( 8s:n4prd y4gi phe 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 lholhya4 0db69t ;f r,pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate thelo4 f06h9, yadhrbt;l average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someon6 n)t0ba*jhqj- 6 7 d:oqgiaede who does 80.0 J of work on it? Ne nqda 6 g)tjjb7 *6hoq-ia0:deglect air resistance.    m

  A 285-kg load is lifted86ztac un7,ic;kj a2y 22.0 m vertically with an acceleration by a single cable. Dekazjt n8ac2 uc;67,iytermine
(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 4 i4zuvn1k 9 4lea9 124jam)e.ev nrovu40N/m How much must this spring be stretched to 1a1a j .v)ev4k9n4zeeu4m 2nvo ul 9ristore 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m hi 9 9zgglp9a9klgher. What is the change al99 g9pzl 9gkin potential energy?    J

  By how much does the gravitational k( -. y o7r(ed))/hxpjsmmxcrpotential energy of a 64-kg pole vaulter change dhr-() k)c s(e7jop/my.x xrmif his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horiz.brrxc iy v), u4.9ehjontal surface has speed v = 65 km/h when it strikes a horizontal ,9rj )cvxry.b .uhie4 coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it3p w3a*j b*oob is 2.20 m above the ground. What is the potential e3*jpoaob w3b *nergy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs toe/* lcmi5ob66 fpj.vq8qtto9 the top of a 3300-m peak. *t/ p6lqc f o8m eoi9v6j.bq5t
(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 w+ynj vxh3d ys)j )z):vertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass iss 3x) +wyvjy)z n:)jdh now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs*p jzu2 v3 8 l-imoa:bf*)ln.xn4awaw a vine hanging vertically from a tall tree in the jungle. How high can she swing u).bxn wi z3l:olw 4*-8anmv f2*jupa apward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionlmx1 k8wycj 0j1ess 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 tejkx 6 8wpel:3c;zd1 a shove up a frictionless 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 kiwvq)d;u; ,cjg netic 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 mass 2.10 m and cw;), dujg vq;cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward iy w43z xvqfnbmj/. +,from the top of a platform with a sp3zmjw qv f. ,4y/+bixneed 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 mp569h s5uk9a6w bjvj its mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed dow9 js55p9uj6 bwa6hmkvn 0.150 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 track sh xqo0t3:bonxf6d ,6rt mn wn3tb9xj65own 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 q x,tmf obrtntwbn6n9 3o 3dxj06x6 5:height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffness cons q1+ jq/syp)tdtant k), Fig. 6–40. The block is given an ini)q+/d jt1qspy tial 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 frb zr2bge)+.l-j +d5 ytu g3wopom a bridge. She is tied to a bungee cord whose unstretchedobr.t)3dup j2 by++gz- gle5w 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 dragge;q p-28cepw 1o.er2uwzi ,x wid up to point 1 where it is released from rest. Assuming no friction, calcu2ip-pzwuo;, 28e x iqwcr1we.late the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is throtg*z9a7ape d;30vwlu wn 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 spru46hh5g(5t aj1ais))f fukyping to be placed 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 spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more ti5 ukhhu4ja a()tfg1sy6p )5fhan 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle/3gt w8 :cvvtf up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in opg;h def- g2 mgp4z (6a bls9zk*jgk6y0posite directions, collide head-on and come to rest. How mu2 l kfagsb9*gypz6-ejmg6d4(g ;k z0hch thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide ot )e fzi7:2kg6jad i03.5 m high and reaches the bottom with a speed of 2.2m/s How much thermaf)zea i62k0:tid7 gjol energy due to friction was generated in this process?    J

  A ski starts from rest andl:j;pnkjvvp *7ru om7u:at;j--u d z5 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 treev7xp5f yii/sh7d2c(. v *ygem 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 bocm6uvmfmf)ya2i.y 0/widnk 8 4b1p w+ unces back to a height of 1.5 m.ify2awfw pcn06+y /um )mkd.mv 41i8b
(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 wit8 b0t)wrkffpl e/4 h5rh a constant horizontal force of 350 N. Fo 8r5r0e bfptk4hw/l)f r 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 coa 0zry y.wl7 s-pz0n-xkster in Fig. 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its 0zxnyy.7lz k0s- w r-pweight, 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 upwaygzx8 rrm*-tlkk) ; njt:c:c8 rd 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 s(i39gh-cniq2:ir lhzom.ag-pring (k=180N/m) as shown i-ggnq:2. 3cl(-ia9ihro izh m n Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly att,nwrrhs2n/m;vk(i6g1 7vkw zwk (k-aached to a very light 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 equr6ws w27-g/zk;r(1 ankmkwvi hkvn(,ilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle u8xw4x8pd ; /qo(zedghcs:4op sed a “glider” (mass of 980 kg including pilot) 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 dzxoq p:8/x( wohpc8 ;gsed4 4resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a six btpr5nsq3m(kf(ig 7-th-story windrg f(7 sbitp-m3 5qk(now 16.0 m above?    s

  If a car generates 18 hp when travelii)f5akv )vlx *ng at a steady 88km/h what must be the average force exerted on the vv))x*l5if kacar due to friction and air resistance?    N

  A 1400-kg sports car accelerates from re0 j/cdx( t1p1 g5 e+exvjvl)xbst to 95km/h in 7.4 s. What is the average power de1/ +bvj501txx(ve)jdc gpxlelivered by the engine?$\approx$    hp

  (a) Show that one Britisdmth-rg725rin2if l :h horsepower$ \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- c+6(k,novo nthours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h in aboutqn7;/clru ,t;htso ,k ,5daey 6.0 s on the level when it is in neutral. Approxima,;uny 7hc ,ad;/stoeltqk, r5tely what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3006:aia5omyy ir/z*m ttuy . a.0-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If 1a 4/y:k e1ihashp i0sthis motion takes 1.5 s, what hs 1e:kyasipi1h/ a40 average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. Whatd6 gn4mp*j3ul jj2v5p ou2npum 46d5jgv3*j j pltput rating (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium stalt**d+ ykrn;xc6ym k-irs in 66 s. The stairs are 14d*ryckl*t n+; xmy-6k 0 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 a 6.0 ta9h 5.frlh*; tvx ih:$^{\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 steeplr64h)o jet 49 coiib7u3kw2z a hill can it climb at a constant speed of 75km/h if the frictional forces add up to 6cj2uw)bii3 6zot7kr4 e o9 hl450 N?    $^{\circ} $

  What minimum horsepower must a motor v;g -p tdbo (y(titxtiy(-,kz6l2ml2 have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coef6y(;2ty(x 2lz btp,(k-lotid-t v gimficient of friction is 0.45?    hp

  A bicyclist coasts downne 5j3pl lzc3z .* a/:nv5juao 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(8km2c69d.8yavkv(sq1f p t ta(nw/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.v9ns8q twaya(1k2dvp.ft 6c (5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground/qc 8m7-g.vnz +ewjgoc(kr2t, and the remaining four shen8 2 mct7oc-(ge/zgjw. qk+vrlves 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, 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 1936 .qh9s njf bt*.w4t;flqr. m5vOlympics shows that his cenb5fsvwt 94 q. m.jq ;rl*t.hfnter of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shvsnj3oyw jv8pj9q )/4own in Fig. 6–39 is to remain on the track at all times,j9nvw j 4ovjp /8s)qy3 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 j rpv (-q,zazu9umping from an aircraft without his parachute openu-z,qz(va9 rping. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg 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 horim m/)pednje*kawm67 +xm c9jw 9vk w56zontal cord of length L whose other end is fixed (Fig. vw9kd5m6k 9 ea 7wj 6mjc)+mmnp* ewx/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 mountain. The climb is maq w+srg/*h i:s(z an;ade in 5.0 h startin:z is(a+*as gh rnq;w/g 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 break-g7nir8 6; ko+qohgqqs when a 920-kg elevator 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 Californtlrwpz fj*f(l) uk 657ia claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the powl zf jruw7tfp*6 ()lk5er needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s an, -jg/ljt z7flo5 yp4sd falls vertically 81 m before striking the turbine blades. Calculap7 s5ol,ljt /j y-zg4fte
(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 coastel3r(k qqmk6 ;1 e jszm8(ifyr1r with a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore fri kr1(;iz km81e(qmq3fyljs 6rction. 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 in/0w zbigsd emu ,pqd9k2 9hc:+to work, how high could an 82-kg man climb a ladder2dmq hdkwgu9 i 0c: /pz,b+se9 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 upward wdp, )bl:e:2 z8swjaw 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 sp4joti7)i n6w 2cwo r 62cyh4/ 7gsxddcring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump os2ghd2i7d 4nww c6y) i7/orx6cct4 jon 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 over a la qbwu7o *ghc9mku5:2eke (Fig. 6–45). He releases the rope when his: kw hcqoe 2u5bg*um79 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-kgh.5 j.8g5zbxxft.mzx f7)ods athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output wxthfz .7d)fzmb.58x5gxjs o .as used to accomplish this feat?    W

  Some electric-power companies use water to store ene qln/ 59y+j -w;zrlfivrgy. Water is pumped by reversible turbine pumps from a low to a high reservo v +njwrifyq-l;/lz 59ir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What 8 sq8nh-iyuw6is the spring stiffness constant for each of the two resultinqswu y8-hin 68g springs?   k

  A 6.0-kg block is pushed 8.0 m up a rougfx(6old*l/2 j6 c 0 q)qgqrgsph 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 3.7 un9yhp:so o0jtnv ab +5 j3mqthy2.12 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional lossen.ohj:1tj 9p 5n 7qy uvb+sy2a30tomhs.    s

  In a common test for cardiac function (the “stress test”), the patient wz,; c vf a: m0;epe:ji76fadhaalks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the tread ;7aem,;:f:pv azfj 06icdea hmill 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 verticallybce c4j)k9ed 6 upward a distance of 500 m, what was its velocity when it left tbd) ekc 46ce9jhe 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 waterc8o gf7oskkt/ p7tp72 wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electrici 2co7gf7/ps t7 top8kkty output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s