In what ways is the wo5bx a e3(-m-chhsrqfgp6 tj,)iehy- gug.*z5rd “work” as used in everyday language the same as that defined in physics? In what ways is it different? Gig egf*se6 g r5,-i (h) thaz pq-c5-.humjx3byve examples of both.

Can a centripetal force ever do work on an object? Explain so p0ps-o a-iat47q9c.

Can the normal force on an object ever do work?zq(00f gan0 ur Explain.

A woman swimming upstream is not moving with respecp a5x*sqm;f5j t to the shore. Is she doing any work? If she stops swimming and merely floats, is work done on he mq5p5*fj sxa;r?

Is the work done by kinetic friction forces always negative? [Hint: Conside(xye sx9uzrrh)xw58os4mn 0ql4u6a 5r what happens to9u hy 0szo5r mqr4xn4 lx 6wae5us8)(x the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though youm8z1ney3bjfi 2 1e pvmwgap -ct:v.1, are doing no wormv-.3p,m ve2 cyj8nftawzib1 g1pe 1:k?

You have two springs that are identical except that spring l is stiffed.n /j/i ftm36mt/ii nr than spring 2/n.fmi /jdn63i i/tmt $(k_1>k_2).$ 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 su6 s7q5r4chk s5y lh8a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, an65ksy ul45 qs8 srh7hcd 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 howzdc;k+g2d0b- 3t kdbw much does your gravitational potential energy change when yo wbgd3zkb;tdck2d+ - 0u jump as high as you can?

In Fig. 6–31, water balloons are tossed fr,,ge47ucrh jvwe :/ynom the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ign/w y4:r ,e7jeh,cuvgnore air resistance.

A pendulum is launched from a point that is 9k9d *qii(1n,u0 5 dn jguncewa 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 l dd ,cni0ui91*ne 5ukw(gnj q9aunch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress thextfwvti2e-(:cu3 5:nf cx w( l spring by preslevut :c n2wf(i(-f3c5t xx:wsing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the 7w az76rrkozh+ 4i)i yceiling 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 ther4 zawko6h 7)zir 7yi+ instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top ofxj*so 3j3uz9 d a waterf93 dso3j* xujzall falls to the pool below?

Describe the energy transformations when a child hops around on a 4ox* : kj-4nlheg5 wubpogo stick.

Describe the energy transformations that take place when a slcj b,)0e*stq t )a;dv.+wlrgkier starts skiing down a hill, but after a time is brought tldesg lcjb )+r0w*),;ta t v.qo rest by striking a snowdrift.

A child on a sled (totalpquub88p )hy lua e:;ze7 ew11 mass m) starts 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 therew;a 1e)1ue87qybz:h8 puulep is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their pvh49gvop f;0 bath rather than stepping on top and jumping down on the other side. Exfv0ghvpb;o 94 plain.

Two identical arrows, one with twice the speed of the other, ab q.jj*+cs9 zwre fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much fartjc +jsq9b zw.*her than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in ter+jos vu 7fle kc69p7w3qbg*f) ms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has too g f679bl*p7+jsuvw )eqkf3c be wound up.

When a “superball” is dropped, can it rebound to a heig w khdp0(c)jqo5/2h rlht greater than its original height? Expladh0h2l()kw5r pqjco /in.

Suppose you lift a suitcase from the floor to a table. The work g,vzn uuq 0h ;b2et*ly1n*ide-+.tzyyou do on the suitcase depends on which of the following: (a) whether you lift it straight y0+ve t n,lh*i 2 bytgz*1q.uend-;u zup 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 pfe*3 oz +ffd-sower needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to+rpo7vb3p8 sf 5hd)ol climb straight upl)+do po385r7s vfbhp?

Recall from Chapter 4, Exa7z/kehcvoch.d9e q/ 3 mple 4–14, that you can use a pulley and ropes to decrease 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?vc 793ckd /he/ .heozq Account for this, using energy concepts.

  How much work is done by thl zf6 r0z,f2nse gravitational force when a 265-kg pile driver falls 2 f0zs 2,nlr6zf.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much wortv-)u- + vt+avv7htpmk is req+ah vu+v-)t -v7vttpmuired?    J

  A 1300-N crate rests on the floor. How much work is bjsocv /r1:4 zrequired to move it at constant speed :rvz1c4 jo sb/(a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crate 1tt .t kn1v x1.(hp hm7u9d;owp0.3 m across a rough floor wit1dmkt7vhn ow;t 1puxt9(h .p.hout acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accwoq1ufr/+ o ;/oj+qcsf h /cz9elerated by a force across a floor at a rate of for 7.+w ozscqqr9+ fo;u//o/hc j f10 s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick :at v+8h wae1gwith mass 1.7 kg, lie flat on a table. How much work is required to stw 1tah8+avg: eack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to- w3l d/jbi ak:5g:rulu.t:u99 a zjem liff objects we might not otherwise9 9j/-5i::weua mtu jzbgal r k.3ud:l be able to liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m *w5o30 bljekmlfn( js, gr3tr6 m6;gzdown a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculr g6r(;lw6eg5ofm,b0nm j*3ks jlt3zate:
(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 reqqo 5;1k/8alhqs (h1tw oqb6n*ssnx y4uired to give a helicopter of mass M an acceleration of 0.10 g l ;5ksy1n4s/ hthw1 x*8q(a6 qnoboqsupward.    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 dis67lqbvy -4g mjtance 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, varies as shown in Fik8 v;icywu0ppm6 . jq3g. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x = 100i vp. ;pju6mkqc83wy 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 partii4 xi m33wywz.:qht2 i/ia/qlcle 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 mlvo bb4ad 9zb1-koq/ *olecule, 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 iss,8ntfy z +ag0t(ijj + doubled, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required tcmo:y11ovs* z;b)cdq k. a8sa o 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 traveling at 105km/du ucv6nv .++yh?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force of 1esufa2 a+*n /h3) pof4plfo5g10 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it oo5npgfapfl hf/ * a4+ue 3s2)leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/f;qbe ed)mu 1;s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on the b e;u)1qmfed;glove?    N

If the speed of a car is increased by 50%,x29za)4rv*;wr eq kf p by what factor will its minimum braking distance be increased, assuming all elpf9 w2)4vqrkr*azx e; se is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, inib7/ ,alz2awv f.opgk n/*0 *9kirysnvestigators 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 speey/ b n.a0krn* vw 2sf g7ika,o*z/il9pd 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 k d+u(b ;1b l3ytl7xfuug is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance durin3y fbl7ux b+;tu (1uldg 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 4mmcif0rwb v:j 0 bo*ncxc/;9 by someone who does 80.0 J of work oi0rw*: m0/; 4cvnb x9fcmbjcon it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m 2adtx tb2vcq2dby5s;h z 16r/ vertically with an acceleration by a single cablsd;q1yt225tx2/b6 rdhb a czve. 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 stiffne i-- zndo7+f 4mhekc5tss constant, k, of 440N/m How much must this spring be stretched to store 25 J of potential energy? -c7e4f+oh k5dn imz-t    m

  A 7.0-kg monkey swings from eqww;dp52wxti7 r6y7jy i1. cone branch to another 1.2 m higher. What is the change in potcr7yyjw ewxip. 1d5wi 2t;67qential energy?    J

  By how much does the gravitatio dbx j15.l p:bnojai*;nal potential energy of a 64-kg pole vaulter change if his center of mass ;pjoinb*5x d a:l.1bj rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal sur u4pm9lzpi* b:lp :1lgface has speed v = 65 km/h when it strikes a horizontaml p*i:9ul1pp:zlbg 4l coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book frolw6ixy-os2f,) /an z nm the ground so it is 2.20 m above the ground. What is the potential energy of the book rzl/iyf-a on xs2 wn6,)elative 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 clim c+83 nds8tasb ng85cobs to the top of a 3300-m pe8 sg8 3d8+obct cs5nanak.
(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 nexm ra:wbv x0qj3n xhi, ,mn5*1zt to a ruler. The end of the spring is nextbnqi1w0jvxz:h,*r3axn, m 5 m to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5(dw,y8e(5dw0 b3.x viy+js :cyqjdrt .3m/s) and grabs a vine hanging vertically from a tall tree i+y8yrd dsv:dwy(cj50 w t(3i.q , xejbn the jungle. 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, kcv8)ea t0il-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 frictionlesba sl7zh/a:*ys 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 kinetem;qd)gon )xn uma4/6ic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with ao/ ) eam;6dxmug q)nn4 speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically us5i01ph r m 3h8qjhx2h6i0 rfkpward from the top of a platform with a speed of 5.0 m/s.ph5j6hh8s20 k0hf1 ri3m qrxi ($\alpha)$ 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/muurpf(emggu n*,hco +*o /d86 isc orm*,+8ufpn ggd6 *ohu(/ eu 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 released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides withoututc5 9x.+ uw fl29trro friction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top +.uct rrl5w 9txf2ou9of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is ath9bgz6 sz- mcq5b6 pn,:ub i( tjxpz09tached to the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an iz 5 q0gi6, zpbnh9zbcb9sup:m -j6tx(nitial 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 bung hukdux4q /fw 0a+pdd+ t/nd(4ee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the sprin +(dfq+ h 4 kdtudnawu4/px/d0g stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41cx,7x f / p 01yvsky zveh;5-su5zaz;n is dragged up to point 1 where it is released from rest. Assuming no friction, calculate the speed zp5nvz ;y5xx a- z s;e1 yu7v0,hsc/fkat 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 33)/:bujv pkyj7d 2g d;b $^{\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 design:2z ; mnvtd/moing a spring to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring,:o;2 tnd/mz mv 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 c x9jc6qib4xg/ge 0 vz q;,cf;wycle up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of ma;kxsgeym : 4:ow(1cmt ss 7650 kg and traveling 95km/h in opposite directions, collide head-on a; w:gy 1 x(o:mtsm4ceknd 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 an. rki nc7jinjo32 a,:mvau: l3d reaches the bottom with a speed of 2.2m/s How much thermal energy d.3,cvrl:: nnmaiu 73ijj2oka ue to friction was generated in this process?    J

  A ski starts from reop-95+lwwb t1 ulbv/v st and slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 k.xi*lvi eq .r- )tpd+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 a heighaf *dszt;m )(o2h:a lct of 1.5 m.ah:dts * (f2almo;)cz
(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 r3 1 hrqptmmn*h n)fn/.rsw4n5est, is 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 fm/ wrq.)rnsnt 51nnhp*h3m4 of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of Ifz.ghn3:m:5 : ygv (xderthpv 4 the average force of fygxrv:z hgm:v p: 3.etn(d45hriction 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 p(ye )s6vwf l8upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light ho07a 9 q0:hh 0)auuajh (cqgboirizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the bl 7h0 bhc9qohj a:uuqaag (i0)0ock and the table?   

  A 280-g wood block is firmly attached to a ;l to*b0)y( 2lexct(xwut u pb qb5g(qr-;f8xvery light horizontal spring, Fig. 6–40. The block can slide along a qgb-w ;2x te bq(x(xt5;bto8r(l)pu0c*lfyu 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 swing?    m

  Early test flights for the space shuskg0z01 9w aba cs-mn(0usi /lttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed ofz 0s-0 bicalsu ka/1(g9ws0 mn 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 mo5u4zg9n3 dirk4non dq;rz11rtor to lift a 315-kg piano to a sixth-story window 16 3 nu91giroz1qrndn k;44 z5dr.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what mvo8a0tgst 4z p0s8k5 wust be the average force exerted on the car due to fra5vozt s pk00 84wgst8iction and air resistance?    N

  A 1400-kg sports car 6116dm 2 oyt sloehp(taccelerates from rest to 95km/h in 7.4 s. What is the average power deliyh11steodo p t2m 6(6lvered by the engine?$\approx$    hp

  (a) Show that one Britis1cn dw2 ;jwc anvdvl;ad17f85 h horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often ew(v(q4 *ifno mxpressed 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 from to 65k3vjn8yn153ua zhe p+ sm/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed nvs1ayz+5e3hn38 p ju to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hb2;xa *4( j6ygn kg1dlru:vzo p motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If tr2,pqtjb(tt:f,m j 1rhis motion takes 1.5 s, what average power was(bt:1mp ttfrjq2 ,,r j developed?$\approx$    W

  A pump is to lift 18.0 kg of water permi( ;r6tdvih/ minute through a height of 3.60 m. What output rating (6ivdti;h rm/(watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium a8e1r+ara-h sstairs in 66 s. The -8re 1raa+ash stairs are 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a sy.+zrw pr8:h6.0 $^{\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 m + q/sgj3 bda-c1ntq-maximum power output of 120 hp. How steep a hill can it climb at a constant speed of c bd-/g- q3s+1njtmaq 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg box aloo0*i p 04pr1xkeiok3dad6 x w2ng a leveldix2x 4p i30kdoaeo 1kwp* 6r0 floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down aslw-ai325 k ))r0xnz u.d ol1ovzbd*r 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/h20pi):ef opqv ) bumpers” that are designed to compress and rebound elastically without any physical damage a:eqvp02p if o)t 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 that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 c1 cmgk)87evx ;n sek8xm 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 required to fill all the shelves, assumi xm8xnskc g;781 ekev)ng 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 Ol)djt y :jhj3c/ympics shows that his center of mass rose 1.1 m from launch point to the top of the)ht3/yjj :dcj 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 frictiof.hmmggsqhhn5 :a 3oawzo0. y8/u4o*n along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of radius rgh0n3mhsqo5.a8h ma*f .wzg o:uyo 4 /.
(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 frf:92eepe7k jlvp-;nvb vw :x0 om an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survi;9n ve0pw 2kv:v-b7ej :felpxved 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 isn5pt2 .bcdxcl tu77 4dpgm: e5 fixed (Fig. 6–4pcl57b2tp57gedn cm ud t:x.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-mv4l75+dxn p v7y3d tfo-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Calculat 54 ndtv3vlxf+7y7pod e
(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 mf 9heow5/9eqr above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in Californiaqs3lw3yz 4tv ) claims that its lifts can move 47,000 people per hour. If the average liftt3w4s yv)3 qzl carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s;w gvhs-cej3so)di2 7 and falls vertically 81 m before striking the turbine blades. C is;h ogj2vs7 e)d3w-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 i-jgbuq*.n4s/, x 8d d*yti qqkj2;hawith a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top,a sn ug*;qdhyi*j2qxtkdi. 4- jb/8q of the circular loop and the bottom of the circular loop is 6 g’s — 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 bodaw9 zst.l5- wv1s3f lgy could convert a candy bar directly into work, how high could an 82-ll1g 3.zw w-tsaf95v skg 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 a2l0n8j7yy v tict94 54helseyngle 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 bathroiowf285: le;gurw8 ulbs*a4 bfqv h.(om scale, the spring inside 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 thu2 hbworu*.:s ;g ff4e a8wib(ll vq85e scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swinw:a: k 4 zfcnk3mq5;in9slt(jgs out over a lake (Fig. 6–45).s j:m4inqt3:5l n(kfkz;a c9w He 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 at80a: yu+6) e*f oim vhd/qiefi;e-gaxhlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accomplish this fea0:f-xi vye/+goehm8*;da f6) ae uq iit?    W

  Some electric-power companies use water to store energy. Water is pumped by rpjwl jgk 3:x18eversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 11jwj3l x8:pkg20-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What is the spryx 7jq5l,tibsgjz sl 2+vsj+ (d4 :*pbing stiffness constant for each of the t 2s4 j7 gylv:x5sz +jib+d*jtl(qsb,pwo resulting springs?   k

  A 6.0-kg block is pushedqm duma4kp k z/tk) /;5c7xc)w 8.0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, c2.sv z fjk ne.*tgd9h,;aks v)ego,r1o )vm+how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect fri, k.jv s,fcv2e+g1;.)k d*vzh9os)no aetrmgctional losses.    s

  In a common test for cardin9c/z2-m9vzwg1 u j*ef sv: hvac function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping a vzh z*v 9w 9euv2g/c:snj1f-mt 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 :3jk5 rue;q*sqbypp20 *mh gpvertically upward a distance of 500 m, what p k 5*j0bu q:; 3*sq2pmyreghpwas its velocity 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 xc99go q,b ft,of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its g,c,xo t99f bqmaximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s