In what ways is the word “work” as used in everyday language the sa dxzha0c-xo5/d3 qehe rt8ow 6)ojh3 (me as that defined in physics? In what ways is it different? Give exampleh(5 oc dhoq t83wx3 az6rho-0e )edxj/s of both.

Can a centripetal force evo* :fk:x: 8 gedqwix3wer do work on an object? Explain.

Can the normal force/qy:rwb l5j m5 on an object ever do work? Explain.

A woman swimming upstream is not moving with udsbs6 lzw06mg +zz9z8; ti0qrespect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done o6mszb9u0d+8 z0giz s;zlt6 wq n her?

Is the work done by kinetic friction forces always negative? [*hgs x--bj .f xr,l8vhtvh1:r Hint: Consider what happens to the dishes when you pull a tablecloth out x18vbx:hgs t* v -lh,rj.frh- from under them.]

Why is it tiring to push hard agaihh7cia4 xjm8l:l b28wnst a solid wall even though you are doing no work?lj i:h wxlbamhc8 7824

You have two springs that are identical except thaike26ne/p kn+r16 omo t spring l is stiffer than spring 6e2o+mrkp1o ie /nn6k 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 horizfhscfyz68 s/wj2q7 0 1jfldt 8ontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and /l7yq 8sfzsfj1d h82fj0t 6cwby 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 oyqc lp(qfp3 m4:zb hjj6, dcp2(3oacp9l (w.does your gravitational potential energy change when you ju6 f bwjq3p: (oll.3( jmpz9o4 2yqhcd(c,appcmp as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all with th cn pyx8 6eowbxz(9q)s9e9 m3te same speed but with different launch angles. Which one has the highest speed on xcozeyn m sqxew69 9)tbp(389 impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest poin; y3u*kdsz,z xp- a,tj5al3njt in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium positasd yazt5 3lzp3jn;*x,-,uj kion? Explain.

A coil spring of mass m rests upright q1ga 2+gquezp6gbk2o ; )3loy on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservk3oge l+q6q 2 z)u;ygpboag 12ation of energy.

A bowling ball is hunghoj40fg77ki i:rivf 4 from the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the oh i :r vij0i4fk77g4fball without pushing it. Why?

What happens to the gravitational potential energy when wateo+o.;yi p wx.er at the top of a wate ioxp.o.e;+ywrfall falls to the pool below?

Describe the energy transformations when a child hops around on a pogos5/csmdv 2iz 9 stick.

Describe the energy transformations that take place when a skier starts skiing d;(h0si ew .pib (/tiuq )t4himow(;i eqs4)m0tu wiphhbi/(t.i n a hill, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) s m/bs1g wd)jq90 plj8jwec 1:htarts from rest at the top of a hill of 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) there is friction (deep snowjcld: b81qh)0egjw m sp1/jw9)?

Seasoned hikers prefer to step over a falla 0s0d d z3i jjdk9)pki)8uzuk03 ki5men log in their path rather than stepping on top and jumping down on the other0mij0z padkj30 8i)k5su u3 k)i 9ddzk side. Explain.

Two identical arrows, one with twice the speed of the other, are fired into axax4y.ew +8 fif*e+xv bale of heifwe x4fay8. ++*vx xay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple 60 qm9j(ydxaf +s0o -n;peen lswinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has p+ de 0 sjo9nyn xalm0-eq;f6(to be wound up.

When a “superball” is dropped j u5qeskz6tt+hcmzt- 2::el3s9ftg7, can it rebound to a height greater than its original heighteft2mtg7:-j5s6u9th3qc k+ ls : ez zt? Explain.

Suppose you lift a suitcase fro1v i+nt 7zowe4m the floor 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, (c74iew1 t +zonv) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the powwx sr7s31-z fwer needed rather than the work.

Why is it easier to climb a mountain via a zigzag .sriw9r- ),(; tuwm; ovhq ltotrail than to climb straight u-.o v smlortqw,wu(h;r )9i;t p?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to nfd:r l t:+yxlyc ,x n poje;8je*,q0+decrease the force needed to raise t0fp;lylqn: n e8ej*+xyxod ,j, r: c+a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-lu5ab-*bbq8tfnf7 z 0kg pile driver falls 2.80 u*bfatl -7z5 0bfb8 nqm?    J

  A 65.0-kg firefighter climbs a flight of stairs 2h fw4vhae9,jb i) bvctn,9o,*0.0 m high. How much work is required?)f ,c,obn*w v4jb,ea9tv hh9i    J

  A 1300-N crate rests on the u)-mcrtf d8c8r+c xq)floor. How much work is required to move it at constant speed (a) 4.0 m along the floor againsdu-r r )m+8qxc8ctcf )t a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (ggbo 7tav.u8mi35fj. horizontally) pushing a 160-kg crate 10.3 m across a rough floor withoutgv.87 otf iua53 bjgm. acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across qxs:b nn8t/(na floor at a rate of for 7.0 s. Find the net work done bn 8(qn:t/sxnon the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kgh h,hbqq 8ump 9eqp pg 9f37rsd .-,h87*heyws, lie flat on a table. How much work is p *9e q8u.mphh7-gwpb8 ,r q79eyhfqshds h,3required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-gv w .7(prc mwngxexvm+q6v 25qp6+. y35 can be used to liff objects we might not otherwise be able to liff. Show that t+pxmqv(x wvq revg6yp2 +.n m65wg7.che 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. )fsii9676tzj0j8r w+ oytjrp6 m down a 28° incline and is kept from accelerating by a man who is pushio+t6r rj fjp8z7 j9s0)iyw 6itng back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of j0g 5gt :dxs1h,(zn1ff m*kwwrxw( u 4mass M an acceleration of 0.10 1k rmnj1,fwxd:gz4f s*u0g hwt(w( x5 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 linearft4nr va,1 nr5 and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as vkkj tn0k 191lshown in Fig. 6–37. Determine the work done by thn 9 1tkkjkvl10is 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 on a particle acts in the5+nr :by s vxx p+z2djke4p+3m $+x$ 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 mnbb1bp*+s) w(b jx dw6,t +c9yol.xcfass 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 dhu0sey yf0 1w8q)( :;myqbvdtoubled, 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 tonpizzx6 n 1berso.e *(0hi,7g stop an 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 travel qz807im )qfykmj+b6oj t36vjy8 ay3uing at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a su1mqs) q,d m5bow whose string exerts an average force of 110 N on the arrow over a distance of qm)d u1sqs m5,78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glo: q0ky0 tzo1ojve backward 25 cm when the ball is caught. What was the avk: zy0o 01jqtoerage force exerted by the ball on the glove?    N

If the speed of a car ixgzt9q -:l)f7w l;q qps increased by 50%, by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s r:tx p9gql fz)q-l ;7qweaction time.

  At an accident scene on a level road, investigators measure a car’s +wlg z)uig5 -zskid 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. (l z)w-iuz+g 5gWhy does the car’s mass not matter?)    m/s

  A softball having a massv)x byg h) xmmu)sb5 ng/18/we of 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate th/su/xwyhven) 5) bg8 )bmmg1 xe 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 r;; msov9k41 /wub wetby someone who does 80.0 J ofr k4/ew;vm ;w 91busto work on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceltq3-mivuh( *a55t7k* alv:rbzkfw bx rmu(- ) eration by a single cable. Determine q f hxbbm* *k m55t37v (u zika-a)w(trrl:vu-
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much muswkarg ,., o q-nh1b3gat this spring be stretched to sag w,-13 rhonq.,bagktore 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is the chanmu/ rj6us ak1ug4h;de+o9. ivge in poteiv+od6e mjk1 au/u4 9.hus;grntial energy?    J

  By how much does the gravitationalt8s .0ac.ot sa potential energy of a 64-kg pole vaulter chansa0cao. ts8t .ge if his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 krq t c;4*c.u7 clw;z,s qws.kjm/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What i;k*c ,csz4ws t7 ;l.jc.wr quqs 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 it is 2.20 m abov; t +rp4ly ((ly l*wu;fozgsz2e the ground. What is the p 4uf lg(t ;zzw;yp2l*oslyr+( otential 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 eleva +fqo xy8c wj-klu4v 9dt(k*m6l.np2htion of 1600 m and climbs to the top of a 3300-m peak. x6 *cld8q wpu(nfto vym . -k+l4j92hk
(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 t79.tvf6,*q obqn 4ei 09l0v umwdkhvoo a ruler. 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 end of the spring, where wiln0webl6d94 h7u q9qkof.tov*,ivv0 m l the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running atc;szyofr9 48f top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle.4 s8ozcr;ff9y 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, 5b/ysr , e(biislides 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 fricp wq,9o34 d ;lre.zc (tr7trgrtionless 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 kinet er b8q6tr1yy c9p;l;hic 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 cenp;8bh; cql6rytr9 ey1ter of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps verticalld z4l0yl3(zmcc:voy. y upward from the top of a platform with a speed of 54lvd :lzz3cm .oyc y(0.0 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 mass), whose spring stiff.mvk k o)0tq.fd.fll*xjya*0fa ,u/awxnj93 ness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when relq)kk0* *l3a.oawfdt9n y.u,/ja xmf0.l vjxfeased?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction ay)*,uab o 0(cb hxyh,clong the looped track shown in Fig. 6–39. If the b0cyy bh,cb (,*)a hxuolock is to 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 attach d-vnt (7-cwkred to the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial displacement k- 7-dtcvwr(n$x_0$ 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*yb bq9i59 2dbhlo; jg is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming i2bdoh q b gl59y;*b9jHooke’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 dpx6bg j :snwbp;1 x22 puclc)1ragged up to point 1 where it is released from rest. s:)ubj2 ; pc pcw1x l1nx6pgb2Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s0yk092 f ne:l/ds nxgf at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of an elevator s. h4acg,au e5whaft. If the elevator cable should break when the elevator is at a height h above the toah4ac., u we5gp of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up 1fzc20qbm0s x 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 opposite dire*pb c:qfrtf)dg/.1ui ctions, collide head-on and come to rest. How much thermal energy irf)d/ftib:1qu *c p .gs produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and rv x*zpxs0 un*:ipfy 8n)ap:1beaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in this process? 0 n*pxzpbpy 8s1a u:*fxi)vn :   J

  A ski starts from rest and slidesf ;)v8qa1b8slra, nhnn3 l-be 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 dro ymx0auk+1- wgpped from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of h4;fz qq,cme4 2.0 m, and it bounces back to a height of 1.5 m. ; zq4,fqc4emh
(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 puk335wj 7tb, chdr0yq /zy xd8mlled across a floor with a constant horizontal force of 350 N. For the fid /hrq5bd03 wczx7 yjt,my83krst 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 /b xe-)gyef4 aFig. 6–41 passes point 1 with a speed of If the average force of friction is equal to one/)bx geye4af --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 jdk h0oft .s/d:t8gf/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 a5wc85 gdn u:wvy 5ugumy ,-gl4ttached to a very light horizontal spring (k=180N/my, u 5m5wcld4g:g-vunw5 gy u8) 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 friction between the block and the table?   

  A 280-g wood block is firmly attached to a verym b4nzld5lv,+ 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 comn4 +ldz, m5vblpresses 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”6vg .oj0omzi. (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 (. .m60vozijgo 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 17z5ik70j (qurs 50-W motor to lift a 315-kg piano to a sixth-story window 16.0 m jksz 7(5u0 qirabove?    s

  If a car generates 18 hp when traveling at a steady 88km/h wha*58de .n cjemct must be the average force exerted onjm 8e5ec.n*cd the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s+ 6ljg dg3dyq6. What is the average pog63qlg6j yd+dwer delivered by the engine?$\approx$    hp

  (a) Show that one Britim8x ;vt fq1-btsh 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 expressedkcmo +n,hb ,k0 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 slw6k.4+q (cz;xj )wrul 9swxf bows 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 car travelin9 s)f(6zxucqxk4;rbw l+ . wwjg at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0x0us 7md+7a ,(r9 qpfg mh.cif h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3y-xw 4 5m5;:oxirn x u,zjj6yd-kg shot from rest to 14m/s If this motion takes 1.5 s, what ave-x46ji, z5yy :;xwo5rmnxdj urage power was developed?$\approx$    W

  A pump is to lift 18.0*i pfv/78k0+ +(:xb6wx ljwi zpfzozh kg of water per minute through a height of 3.60 m. What output rating (wa+ +oi*lhf6/zi 8zkj7 pwvz:x(b0xf pwtts) should the pump motor have?    W

  During a workout, the football players at 0hszthu* 7z5w 9imy;25ujaa cState U. ran up the stadium stairs in 66 s. The stairs are 140 m long and*u j5uywis zaa57m t0zh92;ch 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 yyc6c f9ry3r*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 hibe4* vid3y6;xeh2 kih ll can it climb at a const*eb6k2e3; ihh4xivy dant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepowerl; l 1du6 wqr ib4qf(tq/8irj: must a motor have to be able to drag a 310-kg box along a level floor at a speeu w qid/qqfr618t: l(4jblr i;d of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down as vhuv2kp7- 7ky-: jtg 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 “5mfn /srf:+ohm- 1sms3 ki/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bum:/-sf s +s3hr ok1nfmmpers 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 firsh3 kqu3d1v c15el3n imt shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If t elh3umicnk31d5 v q31he 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 famou sw+pl h mey64cg5te4.s long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass4wmpe t.h gl5ycse+ 64 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 frictio0rul;j vxv.c6 y qgo..n along the looped track shown in Fig. 6–39 is to remain on the track at all times, even a.v;qur06.g xlo. cyj vt 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 jumpinfvlf 78 u/i/pp *ty6abg from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.lt6yfpubv/ p* afi78/ 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 b /dabbz 33.aaa horizontal cord of length L whose other end is fixed (Fig. 6–z.bbadb33 /aa 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 mounwt08v0tbj9ji klo1w2ao5cy( tain. The climb is made in 5.(1i 80bowj 05alkto 2 tvc9jwy0 h starting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above a hb;- k mr9.+z4gbd ufsnuge 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 i/xqamz;09v8y+wzv/v( v knzzts lifts can move 47,000 people per hour. If the average lift carries people n0z8 zqvv +(xykz/w ;av9 mz/vabout 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and fall52 keij kfeuo7b 0(z6zs vertically 81 m before striking the tuzo 7iu(bk6 j20eef k5zrbine 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 loop (Fit6iowml h2. b:h/qe 2eg. 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. Im:ebh .wqoh/2el2 6i tgnore 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 dih 9u (cg4z4*dwl7lcn zrectly into work, how high could an4(wd9 lh 4z*zu7nccgl 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 upwut7:9pt tt/z r mf4n1tard 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, thmhec4zh62, lq e spring inside the scale compresses 0.60 mm, and it tells you your weight is lh4eh z2c6 qm,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 abd- zt8.7 58ylpg sxdgt 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his8td8lsp7-b. g5xz gdy velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a verticr2y- ,j. q uccu0h6ofzal distance of 5.0 m in 9.0 s. What minimum power output wazu,y62j.-occfur q h0s used to accomplish this feat?    W

  Some electric-power com pz):xrqowc 0c2b r w/3,e.wyipanies use water to store energy. Water is pumped by reversible turbine pumps / r): cr03y2ewwobz w.c ,ixpqfrom a low to a high reservoir. 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 sti*k o+yxsn341 t6yz f om.izbr1ffness constant k is cut in half. What is the spring stiffness consta+ist4yfb.y ro3zxmn 61 ko1*znt for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up af-4 u(x 2bjdlt29fja f rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how long widl j,pjba ms q71m02 -(cgme:jll it take to accelerate from 55km/h to 75km/h Assume the power stm 0p7mgqjs -(e,lj: 2bcadjm1 ays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the pa:5ff4s)t;qdan yo ;c rtient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when tq cfs)4n y:dr;at o5;fhe 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 50aaqz5r:/ffz3w7y4 xkv9m /lj0-kg rock vertically upward a distance of 500 m, what was its velocity when it left the vo 35l9 vj7fqw k z/a4famxrz/y:lcano? $\approx$    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 95kr qu.v ;v su7z.7)mxnag/s (a) If this water wheel is set up to provide electricity output, what is its mvm)sr7uv7xa .un;.zqaximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s