In what ways is the word “work” as used in ev y,oi+vg,c 2frg-fex y2 3nm+zeryday language the same as that defined in physics? In what ways is it different? ,r+vn ofg 3z2,+y-ci2feg yxmGive examples of both.

Can a centripetal force ever do work on an object? Expl ajfcliavps; /k* l5tt*23y7xain.

Can the normal force on an object tv/;*6 mcp;njnwau vui09. kbever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she doirzs i 6-te0h(*8 naxlang any work? If she stops swimming and merely r8 6lz ah(s0xe a*in-tfloats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Con s0j.zoedcb:9q8xdd 2zzs7 e:sider what happens to the diss2 .dejczxd0:sd7o :98eq zz bhes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even y)jno qx- 9lhr9 .v3b+btlr6m though you are doing no whtlm 9)boyxqr 36jb9v. n+-rlork?

You have two springs that are identical except that spring l is stiffer than sp iaz4l(s,q6 lk(p8yao ringaks,8 4la zyo plq(6i( 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 blocktj i gd0atn,z7k)b0 d;mut)(h that is free to slide on a frictionless surface (Fig.6-30). T0 )att0bh did;ukg)jmn7z ,t(he 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 potential energy change wh8 0 z2*aatgvl tvu1tw9en you jump as higha*tguv9 vl 8tt 20wa1z as you can?

In Fig. 6–31, water kn 6jm1.q0shoballoons are tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speok n60.1qhjms ed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h a ka9*6 6fz/j9fm ,yro(xnd qaabove its lowest point in two different ways (Fig. 6–32). During both launches, the pon*mq,fyjaa/z69 xf a6( dkr9endulum 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 position? Explain.

A coil spring of mass m rests upright on a table. If y1xfb:r a)pieoum (m1 /ou compress the spring by pressing down with your hand and then release it, can the spring leave the m/mu1:( 1parebixo) ftable? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceili oj ixb2 6rmx74:jbch7ng by a steel wire (Fig. 6–33). The instructor pulls thoir6xj72hbxmbj 4:c7 e ball back and stands against the 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 en+diwthrfd9 1(ergy when water at the top of a waterfall falls to the pt1wd df9i +rh(ool below?

Describe the energy tra+efzdu bz4 k.s*3tx;i nsformations when a child hops around on a pogo stick.

Describe the energy transf qqkte8/n:ng .ormations that take place when a skier starts skiing down a hill, but after a time is brought to rest by striking a snowdrift.tek 8g:n./qn q

A child on a sled (total mass m) starts from rest at the topves*.q*,x4 wsi8y i p++w xhuu of a hill of height h and slides down. Doesv *xy++ i, xw4u8shsueipq.w* the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather thanqukeq/ +0yxm.1xdt i2c; 0k ov stepping on top an/e xqvm0 2 k+oqukx10d;i.tcyd jumping down on the other side. Explain.

Two identical arrows, onnepqp4 woxhh:;-cpldxb+hg ,: ,7a 5s e with 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 p+xx5 :lpcsaghd,p7-e won4 :h,hqp ;benetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy9 f4d +mx hpeav8k0j2v, (a) ignoring friction, and (b) takin v d4kmvejpa28 hx+09fg friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rqt +v- d9u+ecyebound to a height greater than its original tu+9+d vq-ecyheight? Explain.

Suppose you lift a suitfb:lma a/z y9y u.3qh94cou7g case from the floor to a table. The work you do on the suitcase depends on which of thcz4g 93qfoay/a u.9lmuh7yb: e following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather tum4vow l, d/l-han the work.

Why is it easier to climb a .m( 8 54l uzkl-ikqxwwxp** zkmountain via a zigzag trail than to climb straight up?.uwk q-*zll p(mzx kxk5*8w4i

Recall from Chapter 4, Exampl 7 uptpy*sr*./ppjp o8e 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy loppj/*ps*.o8ut 7 pyr pad (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-kg pile x7jxqcv 4vmy b(wfd n 39a9r79driver falls 2.80797x4 bqcn3yx jw(9dv f9v mar m?    J

  A 65.0-kg firefighter climbs ime(7phd04 tta flight of stairs 20.0 m high. How much work is remd 7tthi04pe (quired?    J

  A 1300-N crate rests on the floor. How much work is required to move it at constd*t mqz d yy7r0o(t(a(ant speed (a) 4.0 m along the floor against a friction(dmqt(z ry7(yoa0 d t* force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 16stwrish**1xp( i ;ep00-kg crate 10.3 m across it1 sp0r;phse w*xi( *a rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelera ryq jy3lvx:vboo2hl/yc;qb-3b38:oted by a force across a floor at a rate of for 7.0 s. Findyc3yor vb3 3y/:-v;bjhlo2o :qb 8xlq the net work done on the box.   J

  Eight books, each 4.3 cm thi ovb rgaxxe7 94g7-1xick with mass 1.7 kg, lie flat on a table. How much work is required to stack1-4rb9i7gx7 gvx xoea them one on top of another?    J

A lever such as that sntb cakef0x8*0j.q5l hown in Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of output force0a0jql 5t8xbekn.*cf , $F_{\mathrm{O}}$, 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 )ai. k jr4rfaa()gvv 9a 28° incline and is kept from accelerating by a man who is pushia9g fa.( )4vrvakr )ijng 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 mass79suq s50 t18dckm 0d j8lksssi:5qej M an acceleration of 0.10 g u1qujmsdekqss j l7 0c5d80tsk5s98 i:pward.    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 axisu*oq44 62xtjuy1do wc is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as showpi5jwgpr7zv77*s sye7 .1m w an in Fig. 6–37. Determ7s 7 .we5 zaji1ppmg7r*yv7ws ine the work done by 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 on a partiy7v b ur/v0(ascle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, with mass of5 6 qqziysy,7o $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its speed sm ;+7sue q-x ,q3 rbm fhs:hz+:phs*iincreased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an eldn w6ohg+w,ev., ta (uectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 atmj(/d0s)4p; hjmbnm) pc( f8.j go:g a.gfaop 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow arem7edb: mh q7*jw(7 whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the b7: e7bm jm(war edq*7how?    m/s

  A baseball (m=140kg) traveling 32m/s moves f p2s/fa q pb4y-e8tz-a fielder’s glove backward 25 cm when the ball is caught. What was the average force exertyt 2fpz-4be8qsa-/ p fed by the ball on the glove?    N

If the speed of a car is increase*0*ppf)m:d sm k(wqild by 50%, by what factor will its minimum braking distance be increased, assuming all else is the same? *smpq:i (w*f )mpl 0kdIgnore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s sf1- ibw) nno.zx+ps3b- 1mgczkid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to bbnm -3 ospb-1+g)1nzzfc .w xie 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is o (p-wi qr0a,npitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravitn ro,p0(wq i-ay, estimate the 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-kgy7.+b zzqse zr4zo6t, rock go if thrown straight up by someone who does 80.0 J of work on it? Neglectz6,qytoz.4e+7z rz bs air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleratiqjt6,/r oku *a,.hdq uon by a single cable.j/ quah6 u,*ktqod r., Determine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant .b+5b.yrzm )aa i5pe+t9lxbq, k, of 440N/m How much must this spring be stretched to store 25 J of potentiyt5x9ibbbm.zp.a+qa l re )+5al energy?    m

  A 7.0-kg monkey swings from one branch to anotheoua02;jlj0 f/l d gsax k0 *ziedi15o/r 1.2 m higher. What is the change in l*0 ;5o 0/1lu xdkio afjaz/jei 2g0dspotential energy?    J

  By how much does the gravitational potential enel -ho/yeack 53rgy of a 64-kg pole vaulter change if his center of mass risclo3ea5yk h-/ es about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontpwo3 5rb 53orkal surface has speed v = 65 km/h when it strikes a horizontal coiled sprirwb kop335 r5ong 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 bmq0cye38qke c5,5 me ground so it is 2.20 m above the ground. What is the potential energy of the book ree3m 5qe8 kc0by,q 5mcelative 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 the top of a 3301a iwd,sfm1w e b.buf(33k(u r0-m peak.3s,wfwaieb b((um1ru1f. 3kd
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a ruler. 5 psarb4.i ebhfvni9 :ux 3:h;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 tha .i 4 5nvsbiu:39r;:h epbfhxe 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 hangpm8pf 4c5fkn10oe:n h ing vertically from a tall tree in the ju1pnm 5hkf48pcf0e n:o ngle. 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 f09o+6 8swmsph*mrjt+ 4mr qf, 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 bu9 k(;.b k p3geur8 i0wwyup-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 kinetic energy is transformed into gravitationaf xql8l3 ely 7yix5z2)l potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed o exly2)3iy 8fzll qx75f 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upwapak,sqxb8 lo9g9 o) q2rd from the top of a platform with a speep8 blkq,) 9s9qgx2ooad of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stitmb p+(c 3zdtd.p gfc3jx) l: 5f8-mlgffness 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 wheb pc ptd3 8.m+3 xjgcglmlf-f):(5dzt n 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 shown in Fig.t)96h 5wmlh isodx(u );e* zyi 6–39. If the block is to remain on the track, even at the top of the circt )di*5lx)yem;hh9zi s (6ouw le (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end 8xzo 1p(zg3ox of a spring (spring stiffness constant k), Fizx oozx8 3(pg1g. 6–40. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord who5a8z.z r /yrr:d/0iorzdng-use unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k orzr d0:z 5u-8r n/azydgri /.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–al)q 2d9mjh8rmm t 1;o41 is dragged up to point 1 where it is rele2mt;m lqom j8 h)91draased from rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angle of 330)eq- s8htw yd $^{\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 pj7ta9e: foai r+ wsy99laced 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 stiffness97oe9jfait: swrya 9+ 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 t ;wejder.:b;e:n0yf(x 0/g p *bx pmu$^{\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 di;a.j) q* ;nwv2but*odo paek(rections, collide 2*q *due;v wb) op.ka;oantj( head-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom hszfm8ionhepn*u3+9 -dt 0g8-kkc, jwith a speed of 2.2m/s How much thermal energy due to frictioz kek f *n9-i g-up0o3dm+chnst h8,8jn was generated in this process?    J

  A ski starts from rest and slides down a 22 o+89( f.gsivl4wu()vql a,mwd cwn5g $^{\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 myu 9(*v(4 ktck ovw377kjquk 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 bounces back to a5hl)wb sm062htka 8zjdu 6qpyud/x0 ; height of 1.5 m. u/d0p hay 5;l0s)2wdh 6jt u6kbmxzq 8
(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, cq:7 ihokg9 sc74xi b8is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of fri:sxq7b 97i kcgi8 4cohction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 witm7 n0r6p o2 bb(wk24nmm: v/ fkfzpqx0h a speed of If the average force of f 6bmfw2x/ mnpkr0qn72 fmpzv0ok(b4:riction 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 refbg ba 51;4qwy)dub4maches the foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly atjj e,6fl1ft/2ipc cj8 tached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when comprescepli,f t /f2jc168j jsed 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 attacheiqqe u -12tsyzn+sd)1d to a very light horizontal spring, Fig. 6–40. The block can slide along a table whes1 nytuiq+)qz1-dse 2re the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttltk;61lo *, :,vkofbsvio- yog e used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventual o1tikvv*os-:b6,o kfl;yog , ly 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 atm7;et:cq: w 315-kg piano to a sixth-story window 16.0 m above?qe7 :cwma;t :t    s

  If a car generates 18 hp when traveo3ut(m h+,neoct l98tling at a steady 88km/h what must be the average force exerted on the car due to friction,( oh+l etc o9ntmt3u8 and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7x:lx 6vdxn ,p6l-v.k7rc5l l r.4 s. What is the avera x,p5lk-cxdvv7 .rnlxlr :66lge power delivered by the engine?$\approx$    hp

  (a) Show that one British horsv 8ufi 6 i7ebf)czp+1hepower$ \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 expr(bx8rr q/la hgh) 8dx+essed 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 slows down froxj,uxcnlwk59te4, *2s t+zk rm to 65km/h in about 6.0 s on the level when it is in neutral. Approximatec5249tl t+n ,sk *kxjeu,wxrzly 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 z3q52yu+aim mk0t6g,l;tv bd kp1qztevz;3 61.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this mothxc5cm (n:u, mk0os(cbt4 (llrr +l7pion takes 1.5 s, what aversoc(t:5x 4cml7 +lkc,b lh (unpmr0r( age power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute throu .che;vfj te*x2hb8 )fcs 4s3sgh a height of 3.60 m. What output rating vsh3b2 ese;)c 48hxffj ts.*c(watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium stairs in.sc7s8 uw6rhzifvu+t a )vwm+ayd-2 rz1:w:u 66 s. The stairs are 14i+2v f:1 w 8-avcu:6sz.mar zwdw)7ruty+s hu0 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 clim gqzkn q3.po0*b 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 steyw7/xk iaz 74)pywad,ep a hill can it climb at a constant speed of 75km/h yi ap77kaz,w )y/wd4xif the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor har. 3w tew;()3llwrpkdve to be able to drag a 310-kg box along a level floor at a speed of 1.2m/pe;3tr.wl( kd3r w)lws if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dow 7hju(kxk.1p7 jymi) lgy5wj;n a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpers” tihq ejs9(: .9cgbm p.rhat are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that9jp(bg:m.s9 riehq. c 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 gro6)c: q3m f zfxixr+8bcund, 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 anz:f c)ixxc3 r+m8q6fb 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 Olympics )tqoegk0 2c mj:s+-ls shows that his center 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 t gej +t2-m0 q:clos)kshe arc?   m/s

  The block of mass m sliding without friction along thej(h *6pl ec0nw looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop6c(l0hjw*p n e 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 m+slu b3 34gt bw7k3wcjumping from an aircraft without his parachute opening. He landed in a snowbat +ulg4mcwbk73w b3s 3nk, 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 is fixed (Fiy5+4yau8p mt.z b watq1iian4t6n(. pg. 6–43). tby ain4q(6iapw nmua1tz+4t .p5y8.
(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-hij6tqh pdrj6, kbeabc ()07it*gh mountain. The climb is made in 5.0 h starting at an elevation crj0q pe jbk)t,b(6i76a* htdof 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 i0+hd3ah8 p )cfxpg9dq 7r lo)ys 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 ivyozf l15jeku2b/r*h5b y0i1 n California claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the powe r251ou05f1yy *jvzi/kh leb br needed.$a\times10^b$ W a =    b =   

  Water flows over a daugl+(uafx 1icht2 u8 v6c-0lz m at the rate of 650kg/s and falls vertically 81 m before striking the turbine blades. Calcula0-agcu618(+ xvfh l2ctlu uiz te
(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 vertica9 ur hei,9urg/nl4 iemaj+s87l 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.ilrgu4s9aneu8h+ir9e, m /7 j Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a 8bl kkmr0juaj j h-ak,d1)a30candy bar directly into work, how high could an 82-kg man climb ) uk08 lj31jhkaarmk d,ja0b -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 a bl xd+p z)do;ttto)qy -p,l25ngle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring u;9/k0d) xosev nng:3my i i9oinside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at itsoeu /xs0ognydi; 9:kim3)vn 9 peak?    N

  A 65-kg student runs at 5m/s grabs a rope,*olr .s:eyip 6 and swings out over a lake (Fig. 6–45). H 6l:* iopresy.e 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 athlete climbs a r5zvjyagv;0 ,nr,a8y: n+04v lvjmyuvertical distance of 5.0 m in 9.0 s. What minimum power output was used to accomplish trn+j 5 j 8yvv an,:0 ravm4yy;vglz,0uhis feat?    W

  Some electric-power compady ei50la-t:2yoprhzeef40 6 nies use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. Tor4-6at0l e 5 zye :yofhpi0e2d 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 cf u 36hbbqqcza:s(q/ 7z a+i;hg n d*dl*ll(6zut in half. What is the spring stiffness constant for each of the twoz:cq 3lhsl(qna*z/g( 7bu* +b6 ;lf zad6diqh resulting springs?   k

  A 6.0-kg block is pushed 8.0 m uz)r:b oci qy8 3bp;p197dbz 8smx zc5fp a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/ha b*- ky)et2l )mr6mab to 55km/h in 3.2 s, how long will it take to ata-mly2 bemrkab6 *))ccelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for car2dt jis, 5nld4eecc62 diac function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg pa, e2c id4cln6s52tdjetient 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 vertii(2-7qtlijykw g ,z) ocally upward a distance of 500 m, what was its velocity when it le l,2ki)7q ijg-(toywzft 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 wheej 67jwp:cl3( 1xu,4 mghr ksyr,f t1oul from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to pp4ux hfrr,ocj1lt6gj y 1(sukw,7m : 3rovide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s