In what ways is the word “work” as used in everyday language9lt*u xx24wp 3ya*lhk the same as that defined at 3wpu4*h9*2klyx lxin physics? In what ways is it different? Give examples of both.

Can a centripetal force 50ec w bi;of )p6gn -a0nf0uyoever do work on an object? Explain.

Can the normal force on an object ever do work? Explrjzu496z/k77l inp w3rhi+ud ain.

A woman swimming upst/nca ccongjn+w5- *l/ )mz5cy ream is not moving with respect to the shore. Is she doing any work? If she stops swimming and merely f yn/l)gzj aw5o-m+n/c ncc5c*loats, is work done on her?

Is the work done by kinetic frict/g.i0nj.swzk.yaipmi kh+ 4g 9m1ay-ion forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from under is/-km yj+4 0 mi kagihy9pz.a.wg 1.nthem.]

Why is it tiring to push hard age1menhcs7/ *u(x 9yw1t 4xdqf .us9h gainst a solid wall even though you are doing no workht( fyu/ h.dw q1gcx *msex19usn74e 9?

You have two springs that are iden 0spl5ar)hiy.7(l av ktical except that spring l is stiffer than spring 2aayp(i)kl5vs7. 0hr l $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free))n g;+svcry;a sx k+z to slide on a frictionless surface (Fig.6-30).;v ;ary z)sgcn+ )x+sk The block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy change wg-jy xy5,vafp1t e, ,-xd.x bmhen youaxypt,.,m -byge,fxxjdv 1-5 jump as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a buh2 8pil/tuodj9e.fh :ilding, all with the same speed but with different launch angles. Which ejl o:ih 8ptdh f/u92.one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h abor 1jdiwvf1j-11a8u4 4ojs kwtve its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will causoj 44kajti 8jdrvs 11fwuw11-e it to swing the largest angle from the equilibrium position? Explain.

A coil spring of masta4x t.p;ks/ ymed2b5s m rests upright 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, usingsd aty5.k2; p/exbmt4 the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The instruw2;:6 iuw z.*r drsekkctor pulls the ball back and s*r 6sr;:2w. edw zikkutands 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 eqibb; 5w yos vg:i7-3potential energy when water at the top of a waterfall- 3 i:w;gy57ivq boesb falls to the pool below?

Describe the energy transformations when a child hopsj pw4ry-a k1/z around on a pogo stick.

Describe the energy transformations that take plac/agf4fu*pz(gs9 d f4ze when a skier starts skiing down a hill, but after a time is brought to rest by striking afd49u (ggfz*4/ psf za snowdrift.

A child on a sled (total mass m) l3ftmw1)jz-sstarts 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 wm)3z-jt1f sl is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in t8gz, 3 thlrm+-ok8dafheir path rather than stepping on top and jumping down on akh8o- m 8dlr+t,zfg3the other side. Explain.

Two identical arrows, one with twice the speed ul9 rby ;gl0* ;pz5x av:8scdmof the other, are fired into a bale of hay. Assuming the hay exerts a constanl:9b;y 58mpx*ca g;zlu 0rdv st frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energlc5dl.wp (5+ rm2 s0 wuim4odny, (a) ignoring wi+ un.d50s4r cdlm2 5p(om lwfriction, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height gaf/d jp w 80qljo nq88mg*,g6ereater than its original height? g* 06ejopwnf/ldq8g,8q8 ma j Explain.

Suppose you lift a suitcase from the floor to ak4j* wbq,n2t* nnkz 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) thkqw,az t*n4k j*n-n2 be time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the 9ghf6 4axw+j gl7 uhg4hp16ag power needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climbk7lfdt9 3 iu ft h4l7w2r6v.od straight up i fdu7 7t tr2.4ohf9vk6l3dlw?

Recall from Chapter 4, Example 4–14, that you can vqlby 7xef6wr9k j965use a pulley and ropes to decrease the force needed to raise rkyb j7x 6w65 v99lfqea 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-kg pile driver 1 xg6 )t l1fqipcmfxhw 6;f br*f57vz)falls 2.80 m16;6blpixf vz7x1)f5 gmwf*r q )htcf?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How muc68gx7d5lyc f 81smpa mh work is requir x5m78 mc86 fdlgy1psaed?    J

  A 1300-N crate rests on the floor.cfyg9o( q8 v(n How much work is required to move it at constant speed (a) 4.0 m along the floor against a friction forcovq9 ynf(8c(g e of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the (fvg1d1 j, fqfmovers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor wit 1 ff,qj1(vfdghout acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a fagzq58f6r rkvz.yu:*h2 : pen6,lou h loor at a rate of for 7.0 s. Find the net work done:yu: .naq6 2g6z v*k8eu5fzholrhp r, on the box.   J

  Eight books, each 4.3 cm thick with mass rz/ z7;j z9z am4f*tvf;jz8uq1.7 kg, lie flat on a table. How much work is required m zf;t zv j/fz4zq;a9zruj78* to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 jmqlt/bt a6( n z,9q7ocan be used to liff objects we might not otherwise be able to liff. Show that the ratio of output force aql6nq,t/otbj 79(zm, $F_{\mathrm{O}}$, 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 7v .m+uc.psi6t;slige)0p cwj2kar + 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 culrma+is i.2cpg.)+c ;tpk v 76 je0swoefficient 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 gifza, x wh):z6zrn c+i.1u oco8ve a helicopter of mass M an acceleration of 0.10 g upow 1o68nx+u.ci)chraz zzf ,:ward.    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 distancc:g,wez4iy(o,z;kcm e51 w kip81cn le 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 axhm/i3 hdszmmx86 kdf z3s6(4 ztg 6*xtis, varies as shown in Fig. 6–37. Determinexmm4xmd3 6z3* g h86t6fhkzzs( td/is 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 particle acts in hrnxek2 5 -2szthe $+x$ 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 oxyg zmbu.1* x kd;es*ea2 nz:1wsjen molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its speed in8u.n ak.uitigf) /i4 hcreased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an e3i r)l 5c3kmlclectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 toysg*n3zd r(wb )k/ o9raveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an averauu8(50 a kukh x*c0+5xodqp xqge force of 110 N on the arrow over a ah0 o(* xq pk8+x0cudkx5uq u5distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling mfn3-or0cc 1oefw 4h032m/s moves a fielder’s glove backward 25 cm when t3100cocnwf4fh-r meo he ball is caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is iei1: e hf-pfh5 i;msc3ncreased by 50%, by what factor will its minimum braking distance be increased, assuming all else is the hcs:-pf;im e31 hf5iesame? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s stt/e*ru.h 85azq p c.rkid 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 a*hc/euqt5r.p.8tz r 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 pitched at By the time a2pkhvk3 5sn rc/bm(cla11mf+ d ).ab it reaches the plate, it may have slowedfapvmc 1h(r 5.d1 cmkb n+a2)sl/a3b k by 10%. Neglecting gravity, 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-kg rock go if thrown straight up by someone wi1jxto; -bo- z:wn6s xho does 80.0 J of worowt-jn ; ozbxx-6s1i :k on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically wz4 bw8tb:mf62swo go )ith an acceleration by a single cable. Determin 4 wmowbt:gfz s68o2)be
(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 constan jsl 7yqb(qosc1 qx; wb j41uf.x3m9p/t, k, of 440N/m How much must this spring be stretc;q4j ujqps1sxbw9x /3y(l cq1mo7.fbhed to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to a vgd/wio/6. diqi(:lznother 1.2 m higher. What is the chanl:z /wo6igvi d.dq/i(ge in potential energy?    J

  By how much does the gravitational potential energyk5hu06) n698 atui *zextvn wo of a 64-kg pole vaulter change if his center uu9tnne 5a x0hz *8ik6t)ow6v of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h when it strng2a/p-gvus u5.3bwfikes a horizontal coiled spring and is brought to rest i .bgn53fg2vp suauw -/n 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 g ahcj/qdnn in, ax)(79round so it is 2.20 m above the ground. What is the potenti7n x,h(/jda)9n a qnical 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 elbsa vrscr7jpb*c. +qk1l,c , *evation of 1600 m and climbs to the top of a 3300-mcj1q. cv,,r a*cb+*bp7skls r peak.
(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. The ykebb9 9jcvao 0(2eo0end of the spring is next to theob bev9j 2a(9y0ok e0c 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 (5.3m/s) and grabs a vineoe cbh tsr(9)0(mqc 6d hanging vertically from a tall tr()cdb q (te 0mrho9cs6ee in 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 fr4c/xbh dh*k6 em*0cfq),bts/ rwov r/om rest, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up rrnsq6nxu 8)8a 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 em msfr e9)4mz5hj) 6benergy 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 aem49jh esm6zfr)b )m 5 speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps qr 2va7nuw+*evertically upward from the top of a platform with a navw7+ erqu 2*speed 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 (ig5xgv 4prj0 m0bnore its mass), whose spring stiffness constant is 950N/m is attached to a table and is compr vmx5pj0g40bressed 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(.pwh*yxt. eh without friction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h musttypx (hw .h*.e it be released?    r

A block of mass m is attached to the end of a spring (spring v v (qgj.kz6l:hwne8s2jtp 4 0stiffness constant k), Fig. 6–40. The block is given an initial dis sej .v0hn:j8wgl2z4 6 ktpq(vplacement $x_0$ 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 bridg5nraqepqe4uc1 bze)* l+5 s q;e. She is tied to a bungee cord whose unsre 5 q *+l;czqb)pq1en ae54ustretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up toi, v(:(o d npe.5dcwh5pe-ykc point 1 where it is released from rest. Assuming no friction, c,pc .k 5(d: (e -hdonye5vwcpialculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a spee19q94ae qs18wx0pkm7/t qk kb1rln ltd of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of an.rh 5sjueeou1,.x imnes45; a elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness const se m;u s45 h.unoaei,.re5j1xant 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;l qz6unl 36ti up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kgoj1fxn - uev 3,2ad0p:gsjo3s and traveling 95km/h in opposite directions, collide head-on and come to r:0dvp -,jx1 2 u3saegs3foonjest. 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 ;5 thb ojg4 n2 1y1kbgid3ck)mhigh and reaches the bottom with a speed of 2.2m/s How muchy)1chbg;1 imjk35btd gk24 no thermal energy due to friction was generated in this process?    J

  A ski starts from rew(+csyridt (pcv(z zpz8t b1) nkp)/+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 m above the gr a;,x8od* g,u/ tyuvz8bg:qtoound.
(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 am9cc :nn nn.2;thmn not2/z9a height of 1.5 m. m2no2n:h; zctt. ca/ n9n nmn9
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a floor with a constant h4o cxnwb:+hp ls.kf,g 1v ;h)horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is wb)4 f;hno h+phcl.g,1vx:s kthe final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–411 6ehqld tka9 5 utl47cxvr*.gnta iz; 4m)5xu passes point 1 with a speed of If the .9 lxkg*45ta ec t 6vq 4ldmzt)1ruxn;aiu7h5average force of friction 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 gx3clez)twup6v 0o:tdrve+ zr + ,/,s/s reaches 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 attached to a very light horizontal spring (1qaaq l:)gf- xk=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and ga:q1-lx )afqreleased, 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 kh, ,luatfyk, lp-*5fattached to a very light horizontal spring, Fig. 6–40. The block can slide along a table ak ,l,kt,uy*5lf-pf hwhere 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 shuttj*( z:j l0peiwmukg -i8;ik9ile 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 of 200km/h (a) What would its landing speed have been in the absen9;i-mejugw(i*zi8p0 j:ikk l ce 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 315- aay;:m4y 8xynkg piano to a sixth-story windo:yy8m nyxa4 ;aw 16.0 m above?    s

  If a car generates 18 hp when traveling at a stea:oay 7)h mcar/v e4rc3, znkv9dy 88km/h what must be the average force exerted on the car due to friction and aik ,mznovr 39cyea)4vrh 7a/c:r resistance?    N

  A 1400-kg sports car acce/y9vm e 7ru 5/pd,a2sjxsb7sh lerates from rest to 95km/h in 7.4 s. What is the average power deliverj2hxp/ /9syd m5 u, s7arbse7ved by the engine?$\approx$    hp

  (a) Show that one Bre9yr 0t2 8gfcm2aud p 7w2ms.8wx dw8mitish horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed ikm2- pyxza+ xa*)l7 yqn 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 6j1z 3k h;mgzo65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to kee6hg ;o1k3z mzjp the car traveling at a constant 75km/h.    hp

  How much work can a 3.u1 tbsncv9 6jb.4)rx q0-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this mot /wq0sr3*kp k 3tgx6cyion takes 1.5 s, what average powwk s *ck6q3t/3r0ypg xer was developed?$\approx$    W

  A pump is to lift 18.0 kg of watk*8c0w;bbkto ib;y6 mer per minute through a height of 3.60 m. What output;8i o;m y*b6b kwtk0bc rating (watts) should the pump motor have?    W

  During a workout, the football player9ueh gc98 voqunb n4-*ncvs98s at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and incline 8ogvc94s e8nb 9nnv uu*c-h9qd at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a 6.0 +8+6fy jwsgtv$^{\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 ao/y:9dw, ecfomfh id4g-0,dg,zxwlcm c r., ; hill can it climb at a constant speed of 75km/h if xfm ,/ ;mz weo:rgw-yc0if.49d,g hoc, d cl,dthe frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepo13h4 h:)9amewe vzg ipwer must a motor have to be able to drag a 310-kg box along a level floor at a zphh4aw)9: ei 13gmve speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dow fdgm .sb9y(wxol, 2b8n 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 buwbar 34c065gucp(crl;s khhu69eza+sbzc +7 ilt “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical d g zua6zac ucl96+;+34hb(sw0srce7ch kprb 5amage 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 that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, av8 n /ll:mb;6bzgul(l nd the remaining four shelves are each spaced 30.0 cm above the previous onelvz:ml;g( nb6/l blu 8. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the ur-;/4di8oico1v wya 1936 Olympics shows that his center of mass r aroyu v/idw;4ci 81-oose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along th5ldn-t s*r7djlu .pa (nla .tymf;m **e looped track shown in Fig. 6–39 is to rema-j. ratas.n5n f*7du;d (l*ylptmml *in on the track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without his parach ss*jd1tn(nzl /q99vj ute opening. He landed in a snowbank, creating a crater 1.1 m deep, but snjjts vl/ 9q d1*9zns(urvived 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 (Fx )b .9kv e0xt)dgz) lrjw1rq.ig. weg txl9rzbv ). q x.r1d0)j)k6–43).
(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 mountaihkh7. 9aof 5lkn. The climb is made in 5.0 h starting at an h k7.kaohl95f 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;ulj+n+xjhm 2-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 47,000 z+/1zvq3ona wku/ /e8 b/wspxpeople per hour. If the average lift carries people about 200 uw/z8+/1z e kqv xa/n3sbw/pom (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m before)obkp i 17e8ra striking the turb1)b ro8eapki7 ine 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 cj3s59+z2plqd ke *a bgircular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your sp3*bz2+l qga p kedsj95eed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly inecckrz:):2 +nt um b3rto work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1000kJnbt:r ) e r3c+2ckzu:m)    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 atj l tzyu1o5kj-hkk 8)f q+(-v+xive4t an upward 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 badp*o25bxj, wjthroom scale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 Nj* 5b,x2jpwo d. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs ou*ra cpxbm)9p-v 40 la rope, and swings out over a lake (Fig. 6–45). He releases th ba*r c9)4p0lm xpu-ove 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 vertical distancenh1e, e 2,as)xil /ign of 5.0 m in 9.0 s. What minimum power output was used to accomplish this feat?i )1nxe2ela,h sn i,g/    W

  Some electric-power companies use water to store energy. Wa7 75n5mac v +qyxqd:rtvp+n 5tter is pumped by reversible turbine pumps from a low to a high reservoir. To stocxrpy 7+mdnva5q 5tn:vq5+ t7re 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 sti7dy 68kguduxnqg g95:ffness constant k is cut in half. What is the spring stiffness co9u87:qy gnk d6dx5gg unstant for each of the two resulting springs?   k

  A 6.0-kg block is pusp kbq)lsei5 *na(x 3)shed 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,zdwjsxj26 i (* how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglec*ds 62wzxj j(it frictional losses.    s

  In a common test for cardiac function (the “stress tkqb9q) *e n9gr o5.fzptt; 7jpest”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg p7bfptqeo ;.9rqg pnk jt*9 5z)atient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distance of q)y9y qsvg4ex m6ci8- 500 m, what was its velocity when xg6eq-vyi q y m)4cs98it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 95kg/s (a784lnjofk g c2jng31z ) If this water wheel is se3 2klon jzcg8f 7gn1j4t up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s