In what ways is the word “work” as used in everyday l:g yukkn5vvc*,3 wg1panguage the same as that defined in physics? un1k3 *ywvcgg,v p5k: In what ways is it different? Give examples of both.

Can a centripetal force ever do wor4jqo6sn44w/nm/ zxh p k on an object? Explain.

Can the normal force on an obje,8f3n j3.lv*na ylj ihct ever do work? Explain.

A woman swimming upstream is not moving with respect to xy s9gqf lqx95ot-)o: the shore. Is she doing any work? If she stops swimming and mert oyq of)9q-lgx s95:xely floats, is work done on her?

Is the work done by kinetic friction forces al)rrfyse f* uh5hjy2fw :/s;r0h(ztk 9ways negative? [Hint: Consider what happens to the dishes when you pull a tableclo*hfzsy5rjsr h 9; )h(u2e:w y rft/kf0th out from under them.]

Why is it tiring to push hard against a solidis v lqlzo: /-;hu-v/s wall even though you are doing no woro:szls; v hu//-- iqlvk?

You have two springs that are identical excepu 5cc/:kuy)2 8m.-kbospecqw t that spring l is stiffer than sprinq m:c-/ o2u 5)upsekc8 .bywkcg 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 (vo wb wmu5qnr:/l cx)cw4* s4that is free to slide on a frictionless surface (Fig.6-304c *(wc:v lsqub4 wnw5/x)o mr). The block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational kmsrs0kl83:s.n d cyov;u4ss07fefd7-s fd ;potential energy change when you jump as high as 7 k-cm;f srs4;0fns8 v.ukdss3sl0d d:y fo7eyou can?

In Fig. 6–31, water balloons are tossed from the roof of a buildio1b eywt,3d- wng, all with the same speed but with different launch angles. Which one has the h w,wd13oebt-y ighest speed on impact? Ignore air resistance.

A pendulum is launchedru9 py0h 93mxhsc :f5n from a point that 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 0ysxup mh9nf5h c39 :rdirected 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 tablo8at vij0r z,ri;s. .ye. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservationi ;rai.o8y vt.r s0jz, of energy.

A bowling ball is hung from the cel w(*5dgwftly: oen; n3-ro;-k6iygvbp-0 hz iling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against t:z-y p;yn -63leho50rf(g;*w kl tbw-d v ongihe 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 energy when water at the top of a waodsww8kde pqx .bs38 t3:,y+yterfall falls to the ,ww :dt3kdq8.yoyx3+bs 8e sppool below?

Describe the energy transformations when a child hops around on a po dkt*5zs 00vdsfp6u, kgo stick.

Describe the energy transformations that take place when a skier uodm /93dx,n bstarts skiing do9 mod/dubn,x3 wn 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 of hui pfroi(+fj/+p17ad eight h and slides down. Does the velocity at the ( +aid /f1ju7or fpi+pbottom 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 to4 -.gjpsaa g 3mz2kj7o step over a fallen log in their path rather than stepping on top and jumping 27g ag 3mjk-.zps4oja down on the other side. Explain.

Two identical arrows, one with +gelfx9uvl64 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 arrow? Explai+glfel xu9v46n.

Analyze the motion of a simple swinging pendulum in terms zbr )*txnxdc8k8 oe 6ul2xi*5vzl e+2 of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to be wound n*vl5ezl2zx xb*ot8c+28x)u e6rdikup.

When a “superball” is dropped, can it rebound to a height greater than ed9rrxv, a6d 8its original hdav ,8d6xrre9 eight? Explain.

Suppose you lift a suitcase from the floor to a table2m5r.owl:sow b 5 orj.cu */d7j,scf k. 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) tho 5/uwjrw.dcs*c,o 2kmrosflb:j .57e weight of the suitcase?

Repeat Question 22 for the power needed rather thag94+a pe )cqxvn the work.

Why is it easier to climb a mountain via a zigzag traill.c9 /pkywlx nx)3 vk: than to climb straight upkxn .9l:3p/ )v ylxkcw?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to dej; hqfb6t1:krcrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Acb6f1hrt j: ;kqcount for this, using energy concepts.

  How much work is done by the gravitational force when a/o .+wa-exl gl 265-kg pile driver falls 2.80 m/a.ellog +-xw ?    J

  A 65.0-kg firefighter climbs a f1v+q gpkt /jin0yo+h7cwl)f57l :mk zlight of stairs 20.0 m high. How much work is req qkvm 7igh/zc+pf o 1: +jltk)nw7ly50uired?    J

  A 1300-N crate rests on the floor. How much work is required to move it at c 2o2av pr9hh u,ng y;qbv,7*lionstant speed (a) 4.0 m along the floor against a friction force of 230 Nn ,a;* hygb 2rlho9iuq pv,2v7,    J
(b) 4.0 m vertically?    J

  (I) How much work did the move 8e*:wx+ anyscrs do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor withouty sec8a +xwn*: 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 ra lxm7y a1:idc.y0ma 1rte of for 7.0 s. Find the net woi.mm:ya ax1 0d1 ycl7rrk done on the box.   J

  Eight books, each 4.3 cm thick with cxn.jz)0hi )/( gcb wemass 1.7 kg, lie flat on a table. How much work is required to stack them onheznbx g) j(0/i )cw.ce on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liffza7pv9.k q3 i9r9lyse v4oth. objects we might not otherwise be able to liff. Show that the ratio of output f apz3s94v.7kvehilqoty 9 9r .orce, $F_{\mathrm{O}}$, 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 f rfc4 +sntr;;hrom accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic fricti;+nft;rs4cr h on 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 helicopteapcld8pf,6; br of mass M an acceleration of 0.10 g upwal,dpapb ;6 fc8rd.    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 s:+pa v, hfptm r/)ji2the 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, va ec,,y2g (8zdfa 5dhjuries as shown in Fig. 6–37. Determine the work done by this force tjdg(a 5,yc2e 8dzfh u,o move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle acts in t o5 uenlvfuqf4)/xj5 wq,clqs9 q27p0he $+x$ 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,da 2opoz:px2 m.m q31y an 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 is doubled, by what fa.g r9/r 4n( lf u,aoodnstk ff-qq/b3:ctor 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 electron 8hrw(n/i w,( qp:y-5akqza 5m-agcip $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 acm 3k 9pol5 +/bcwxcn4m3q8tz df )w:nt 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired f2k r.zm 7m3csqrom a bow whose string exerts an average force of 110 N on the arrow over a distak7.3s mqmrzc 2nce of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fieza 3, qbylwh*.lder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on y. z,ab3lqh*wthe glove?    N

If the speed of a car is incru wlx6bdj);do f27pyiw/4l/tc5bo z3 eased by 50%, by what factor will its minimum braking distance be increased, assuming all else is the sabp;xw) l 7tjcubl/yz6fdw/ 5i o423od me? Ignore the driver’s reaction time.

  At an accident scene on d 8p uro5jv.5r ,hqm+b4jc 9ok./7ncnr,gaqfa 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 estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car/bk9 m.g4n5,5jrq rccda 8r f.jv,+qh7n upoo’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitc;/)q ai *2ymev-,2wq hgg. rl9insxdv hed 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 the d.*ia m)- d,/v wvqg2isglhnq;y92 exr istance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-k vjl-7rn250utcv-s1pge os1 vg rock go if thrown straight up by someone who does 80.0 J11j-grs0cvsvtpn - ou v25e7l of work on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vm;7 eqoiuc:567egq7 ez 6o dog*lvn9eertically with an acceleration by a single cable. Det ;e *mo i7oeu6e g:6cdeoqlgn97qz57vermine
(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 co*(zor1t g)v e:a/ mlz91(mskrcm* d wnnstant, k, of 440N/m How much must this spring be stretched to store 25 J co9:vtw z(gz*/al*srr)me 11 n(km dmof potential energy?    m

  A 7.0-kg monkey swings frq (6al0au( kjrom one branch to another 1.2 m higher. What is the change in potential energy? r0(qa(6ul jak   J

  By how much does the gravitational potential energy of a 64-kg pole vauk 1,i,kndj;g9 cr/nq 7 r5p+ bqai+jwelter change if his center of mass risesik9q7prnbcke j ,g+a/; ,nd1+riw 5jq about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 6c j e8jtz g9qm,iit;;75 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffnct9me ;7q8jti;i z, jgess constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m above k:ql (ppe3g1 uae/hj2thgp2/u( pa1kl:eh 3jqe e ground. What is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs to)*zrp ic 0s9nc the top of a 3300-m peakc) 0z* ncps9ri.
(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 r:8;0vcj3 voqcoik r z*uler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the iovr;qocz3j80:k cv * 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 a vine h efgm /sv lui4pl,p*l/p.0od(anging vertically from a tall tree in the jungle. How i0 p.lp/m,lo/f 4 (l*esvgupd high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, star-uinhdu g8z4u/c+u.nting from rest, 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 frictef zw2nd17e5l+ 0ql4d7vbw(i nka0 h8;up opdionless 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 transformed into gravitational potentp jl:ae-h 1;k) pa bgnszp59u5iale pa;p khb:l5j-1 ga9 p)sznu5 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 with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps v1xlnkr8u..;u3g gemsu 5k q9dertically upward from the top of a platform with a speed of 5.0 m/s. 9 kmx u5l.38 d.gru su1gqk;ne($\alpha)$ 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 950N/m i -8.rznu(i poys attached to a table and i 8-pr oui.(nyzs compressed down 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 g/(s/,.m z,gjuuo dq) 7xummf looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must itfz,m/,u/g7 odgjq .us mmu(x) be released?    r

A block of mass m is at/3x*-dd kluujqxvm7- tached to the end of a spring (spring stiffness constant k), Fig. 6–40. The bu*dlk37 /xq dv-mx-u jlock is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She 25 rdn:m32 s1b qvs 4r/etruajis tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffn:t2js4darqrsb r 3n/e5 m2vu1ess 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 iniz-wj(eg cr / j82wd0g Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no frg/-c0(wzd grj28ewjiiction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at1 7ct5v :1 1rac3pfc ,v5dbgtvnmue kzm(2i0s 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 pl/; zq1j,lruaa69us c oaced 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 t91z c oras/ q6u,luja;he 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 7.8 k5xt2n0-nln74e cge4q pqh2 d$^{\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 oe6vcim64b1rv p x.0 -)ksevavpposite directions, collide head-on and come to rest. How much thermal energy is produced in thi-xsv bk4v6 pa1e0r.)cvmi6ves collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the botqszn8s+i: j uwre 8;k;tom with a speed of 2.2m/s How much thermal energy due to friction was generated in this procek+s8n z;uwiqjr;s 8e :ss?    J

  A ski starts from rest and slidnxp jx* ryih8 btfa*5-*2 pk7z,d 6ebses 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 m above the ground. wj4 e.k (zkd:ue(* kqh
(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 bq7+m vzgvg b1;(o 7wefack to a height of 1.5 m.;7gveqo zg(w7b 1fv m+
(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, start-4arejj tz24t2dtf 8ling from rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and forj2je- zt2 d8a4l4t rft 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 Fioz twrm2:7ht9 +;kprr g. 6–41 passes point 1 with a speed of If the average force of frih+t 7zpw:trr9mkro ;2 ction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upward 1ph y5g 1n65gvb-uad1s8.0 $^{\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 fir-qev dylf:-/ao;nkm -: yts)lmly attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when; ldmlays n:qyvkt-/- :)e-of compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizo6xky87uhq) v7b3 mss7):fr pkz mnvh( ntal 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 equilibrium position will it stretch on its first swinp )h kmu h76qkv )r:7fsm7 ysv83zbn(xg?    m

  Early test flights for the space shuttle used ayo;(wtrhf9 m/ “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h f/ (mt;hryofw9rom a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 3gyaz *q0k;rpo0 f4qoo :7 6cgn15-kg piano to a sixth-story window 16.0 m abq4ooa0ygko:7f gc 0*rpz q;n6ove?    s

  If a car generates 18 hp when traveling at a steady 88k vbbn+nbe 6z/ itvsi, 51)hew1m/h what must be the average force exerted on the car due to friction and b,e1 )1 eish6z5vnbti+ n/v wbair resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. Whatdm o8mi slrtz /+).8qs is the average power delivered by the engin8srom zq l/smi+d.8t)e?$\approx$    hp

  (a) Show that one British horsepopyxgp61guy22 wer$ \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 exs 2pbcb0u9;x 2 i ;zffd;qho;rpressed 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 sloy,-hkv1;p+ut:chh ;s l v,nvj ws down from to 65km/h in about 6.0 s on the t+j;,h hyvsvv, p ulnc1-;h:klevel when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 hk5 s,y *39p)dzy.q phyl 5pvpf? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motion takp alf/byq1xsze4s.;7es 1.5 s, pea7z q 1f4x./; blssywhat average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a he1/1ots u;xm*fe uoysa18 8czeight of 3.60 m. What output rating (watts) shofu8est;uc*s11za/em x8ooy 1uld the pump motor have?    W

  During a workout, the footlv63- bx a9wlkqpo+9 59dydsnball players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an l5 d-qs 3vwpyx99baln9 d+ 6koangle 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 clilqqk p 4t9he4(io- 7pawx vd8+mb 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 hi n, j.erx cyyn,wi+nqxy.9p8:j sj27wll can it climb at a constant speed of 75km/h if the frictional forceeyjwj+c:yj nw82y qs.nr. ,p,nxi7 x9s add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-ky2u-so9d+ szh g box along y2h dss-uo+z9a level floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dow,t y sqzh(*oe2eavx,p k-o-0wn 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 carf4xgobsg.10pc s0aw, s have built “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If. 0gab1g of0cwsp s,4x the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the fihw,z0gq:mm:dmbu sm68 ln. + orst shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is mm zs6wgh8:m+odq 0,mln:b.u 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/:a6 hnnqnqmg )qh4v ; 1936 Olympics shows that his center of mass rose 1.1 m fq;g:/qvn h )nh46q amnrom launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shown in F:avn+ o jpn,5vig. 6–39 is to remain on the track at all times, even at the very top of the loop opj,n : 5v+noavf 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 fz-.6zw6j s daprom an aircraft without his parachute opening. He landezwz6s-a6 j .pdd 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 horizontal cord of length L whose other end isonce; l eswxsyj.7/9b.e r ;,dog7 rn/ fixed (Fig./s;cergy.elo.n7; ,/ nb rwse7jd9ox 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 ofc 3 lst ln(au);j:ks8e a 3700-m-high mountain. The climb is made in 5.0 h starting at an elev:cllt nk sse3a)(j;u8ation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above a huge spring (rue d;dc,n)x3x. v du8$k=2.2\times10^{5} \mathrm{N/m}$) 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,*t ao2dgl: teq7q;6 y*hbcm0y 000 people per hour. If the average lift carries people about 200 m (vertically) 2yh 6ya7:*gtbt;l qo0m*dc eq higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dmzo ke9ce i v40im,f 9nu/:er/am at the rate of 650kg/s and falls vertically 81 m before striking the turbine ieof94z9k v/ emur0n ei:mc ,/blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical lrlc0lc.ayui+ l t* *3boop (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 —0yl*lbrtcui+3a* . c l 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 f2 jhp:+g kol9w j gkxd4/n)6mconvert a candy bar directly into work, how high couldl/j2x d6:ko gwjn9 p kmhfg+4) an 82-kg 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 upward angle ofh)t kfaqfl 47* 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 compresses 0.7 zjgd1da df07kn7eh x,3msc/y; r ;cp60 mm,khdr ,c x 173ga/ndcymsfz0;e ;7j dp7 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?    N

  A 65-kg student runs at 5m/s grabs ah6+(( mfwnn dm 1iszj2 rope, and swings out over a lake (Fig. 6–45). fmj1( znshi+n(d26w mHe releases 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 ,rmsozrisc5 ywu+yhx9o 8jym;-p0h1o bb*+ ; athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accom0 co 8yr 1y;wohu+,s+ pm5zx9hoy bj*r -sbi;mplish this feat?    W

  Some electric-power companies use ,cks;xyoejsc a58b- l(rv 4*f water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store thecj-vs;8sf 5 lxr ky* a,(b4coe 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 stiff6,byojzh c; 7iness constant k is cut in half. What is the spring stiffness constant for each of t h6zbyi;,c oj7he two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m upxgg15ujxz ) /x+5bi obua(l9z1.kq v d 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 accatm 5g.fg+sniky, )e9elerate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays n e)ytfsk59a i.+g,mgthe same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walkskp1d1wr0al n3r*b0ik3 v /3h,sljju a on an inclined treadmill (Fig. 6–46). Estimatek3kih s ru*w d0p3na/,0blv1al jr1j3 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 distanc kk)s+olgp g.n8* db5pe of 500 m, what was its velodlg* k pbk.8gn)5 +sopcity 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 0j./b/qj f/zb)moxkg rate of 95kg/s (a) If this water wheel is set up to provide electricity output, whqf j ogb0x )zbjm.k///at is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s