In what ways is the word “work” as used in everyday js gckj:z c6 3e6sb*m3dc 8u*hlanguage the same as that defined in physics? In what ways is it different? Give examples of b mbj6hekg:63j* s3*8u cdcc szoth.

Can a centripetal force txs (j pb3p2)q7; netqul )voo5-9eqo cbwm5 6ever do work on an object? Explain.

Can the normal force on an:z t+u3)vvl 3qr3mdbm object ever do work? Explain.

A woman swimming upstream is not moving with respect to the + nyd3aentk ee70*)wbqb7 ,a ashore. Is she doing any work? If she stops swimming and merely floats, is woa*b +3ean0)w n a k7ybe7,eqdtrk done on her?

Is the work done by kinetic friction forces always neg9 us/m)v6k edol 1dg5bative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from u bu1ld g95o)6e dskvm/nder them.]

Why is it tiring to push hca ) xt9prl.-sard against a solid wall even though you are doing no wa).s t lc-xpr9ork?

You have two springs that are identiue38 yftid3k-d x wd-0cal except that spring l is stiffer than spring dfd- u-iy k8ew3d30xt 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free to 6ww4;hb0vz xv4sw +v bslide on a frictionlevb6; +w0hswvvx44wb zss surface (Fig.6-30). 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 )i.x :,gxxaxj change when yx jgx:ai)x ,x.ou jump as high as you can?

In Fig. 6–31, water ballorrfdz*t:ekv xkoi0j/8g5( /z b tft 3:ons are tossed from the roof of a building, all with the sav (o0 :k/b/zie*:t r 3zjkfxtt dfrg58me speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h62 6d q*zywieo 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 they6o6 2id *qwez 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 you 6ovnr- az5cya(sa-s,u5 r2r wcompress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, usw(acroynz-2vua-r6r5, 5 as sing the law of conservation of energy.

A bowling ball is hung from the ceiling by a ste0 c6a z(5ooehael wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the baoeaz0 ho5 c6(all against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top of w yb6j6fe5)0vhs1v heq+vh9n a waterfall falls to the pool belosv 6e69e1v yj)hbh5vf+wn0 hqw?

Describe the energy transformations when a child h9*bgv7rtgf*tw l)zdntb1 / *f ops around on a pogo stick.

Describe the energy transf9, b pssyxn1x1ormations that take place when a skier starts skiing down a hill, but ax by,pxs1n9 1sfter a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of heigq1zi/ ko35-f0bcu9s/9kh lz dz :pe7o an kwd6ht h and slides down. Does the velocity at thbkn3ckaozeo /- 9d p61/:f z95 hwszdi7uq0lke 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 ra +z4/c )n/(z vppyva-pmsl 8vrther than stepping on top and jumping down on th/lvpcv(a4+ - )v8psmr ypnz z/e other side. Explain.

Two identical arrows, one with twice the speed of the other, are fiigbb 2 zc2yl:8red into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.bb2iycl 8zg: 2

Analyze the motion of a simple swinging pelveu 9 d6ov+j fa8*c5bndulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain fj* v5+v lcbo6e8d9uawhy a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater rw 4vw,s0lf 7cf:qf ;sthan its original height?7r;f s0wlqvff wsc 4:, Explain.

Suppose you lift a suitcase from the floor to a table. The wor9fjbf) :g*k0rcz2c q8ojxk 2lk you do on the suitcase depends on which of the following: (a) 22c8fzo bgr f:*qckj j 0kx9l)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 j3kaf7cook,- fp6xo * *ung0irather than the work.

Why is it easier to clie+xlp 5e j42p 6;md3xyvd j;f gwosd,7mb a mountain via a zigzag trail than to climb straight up?;ds 7m, y +d;jopexl5p g3v2ewjxf6d4

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes gqwpux+ ) 2q-fys4nu2g+ pm.k18ub ymto 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? Acc21mm b 2w q4gsk -u8u.p)nyfygp+u+xqount for this, using energy concepts.

  How much work is done bv wg zax,sf;6*y the gravitational force when a 265-kg pile driver falls 2.80 m? ,fw*6g; zxa vs   J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work ogxy.hx+ :f /qis required. :+y/qx hofxg?    J

  A 1300-N crate rests on the floor. How muchnoi 4noly6sb ,e9.owe6(ve e73vw jg+ work is required to move it at constant speed (a) 4.0 m along +7e ve w3 6.sown,4noejgeyo9(iv6 blthe floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) phfxx/1/ fun8fdwnj0 t )uq.j2 ushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the ujf.n81xjxd)f f u 0nt/qh/w2 effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across al*d.htnx+b y e2 nj2;j floor at a rate of for 7.0 s. Find nj.hlj tbe 2 2;*+ndxythe net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 k38t3 mvy6:n/j( xjl wl79 jy (at2zxz 8yzxlnyg, lie flat on a table. How much work is required to stack them one on z3a(n/:tyx 6 y72(ylx8nj zwxl98jv lj3 yzt mtop of another?    J

A lever such as that shown in Fig. 6-35 cwgf+l+j6 yq ck:s.a,3 0ytftu an be used to liff objects we might not otherwise be able to liff. Showcgq:yj 6tl0yt ua +w,+3.sffk 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 down uh:+2brivt e tv0 fy)9a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to ut :yf v)90r+h2eitb vthe 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 hepg6qx m j 5xu9,vp4t-rlicopter of mass M an acceleration of 0.10 g upward. ump-g 96xp 5v4xtjqr,    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume the distance axis is linear and t2g ;i*ndom rk,hat $d_{\mathrm{A}}=10.0$ 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 Fig0jagt,g rl7 1x. 6–37. Der7a,gtg l01jxtermine 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 actsy* mbbb4hlu8( 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 ocffh,2vx fylcz ,c(6wg iu (+-isj,(txygen 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 inpf v3/be .dy-ycreased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is require8u1.irqfftl 5 d to 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*p*y d9:eyxaly) q)2ojo+nc z done to stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exe l9b4jz8l/9s zjne0 xmcsnhoc* + /c9rrts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arroj xmc nc* /olz9sj0ez h/ncr8ls99b+4w as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glov;ec wgqe0 /xx;e backward 25 cm when the ball is caught. What was the average force exerted by th/ eex;;x qcg0we ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum brake75exanfx 3b/(as-o1 fr -u xuing distance be increased, assuming all else is the1eoux7- x3 sbxf5a/ e(-rfuna same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure z 6sintyv7s,m-zc7/ s*d n p2wa car’s skid mark to be 88 m long. The accidennts,6npv7sz*-ysdw/ m2 7 zcit occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By th,m7-7 vrjpz8redy , qce time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during ,q,mrr j 8c7yze7 p-dva 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 some0j7f,l.c n)frve. t-ou8rh kjone who does 80.0 J of work o rjfr8j.l),t . e0 cf7vun-kohn it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an accelerativye9pq)d1 q*i( z-ffjon by a single cabz -dfe19)q(y*f pi jqvle. 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, k, of 440N/m How much must thijbu./wc5 6htts spring be stretched to store 25 J of poteb.w5u/t hjt 6cntial energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is the chanc;nrcjydz yi 6a8uc8;ck 86x-ge in potential en;8zy; j8i cx d-ayunk6cc6r8cergy?    J

  By how much does the gravitational potential energy of a 64-a ne mjxw/57:z/yp. amkg pole vaulter change if his center of mass rises about 4.nm/ezw/y5.mpa x 7 :ja0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has g *v+k6h0 +j l jfuxndc5-ov7hspeed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffnod+vjc gjhu7fl- hx6v+5*n k0 ess constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground s mqox0z+uk6p 2f2c1dv o it is 2.20 m above the ground. Whok d 2m+v1fpz q06xcu2at is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs5u ykha 7sa/)eg/k7bj to the top of a 3300-muaa y sj/7g/ kh7)ebk5 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 ne0k8s; .)xdkoq iw. unoxt to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spr8k. kodnxsoi0w ;u q.)ing, 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 gra hqnkbl o+da/5.0prw:-5 jqgy bs a vine hanging verticalld.qg/o 5n+qb5hajkp w -yl0 r:y from a tall tree 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 from rest, slides down a frict6; . 04v )k6mhfoqveecdx7fd b b7yts3ionless 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 b6y)9jlb)/+ap f blz xa 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 et. +qem ln4e-k46ah *vo/uk.d9pi //hesl d jvnergy 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 kqnvl..uv *+ ats//h4m6 /oklh9edjpeid -4ewith a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist j835n lovjnp 5tumps vertically upward from the top of a platform with a speed of 5.0 m/s. p8tv nlj55 3on($\alpha)$ 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 /dxi a5nw8 1wi 85kmy arvm-r6gjh0h.psi;4 s its mass), whose spring stiffness 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-h 8n8j 6s1xmv pw.5r4m ;sa5aihdk /ygiiw0r when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along 7f1x ih3zkij6 2y)wqzthe looped track shown in Fig. 6–39. If the block isqh y)2fxi73z1 jiz6k w to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffbg n79 rv bvl2824 oad6k.qokrness constant k), Fig. 6–40. The block8a9d4bqr 7n2 kv6rg2oobl .v k 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 bridgezqa plv:8*0 loe( 3kng. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law alnvk3 ( ae0*gplq:8 ozpplies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car 1c)o .f:ug p jazc88:btwne2wshown in Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calculate the speed oj8zaef) w2n pw:u 1ctgb.: c8at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with )za)hd-*0+0giz ,ajydldqt9e qs wy 0a speed 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 t o oc16oirj)g8 mgw9:4xmp2aho 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, 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 passengers4 mocw 8o)gj2r:xm6 9og1pa ih.

  A cyclist intends to cycle upz+r;h.;cx59 dbjj d /cs0sflv a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in opposite dir jrd; gl)s4p-dections, collide headg4ldspdj); r- -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 o/vr4wg z:tm f,- 0yo1xoxd4ga slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in this processog4 f0om:v or ty1w,-x4/xgzd?    J

  A ski starts from rest /jjpu6df, xt-i1- irband 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 ri w,*z5-xx yt m7d2st+*otluground.
(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 li1uei:0ug xlznniib ;)5l5 phks++8m, and it bounces back to a height of 1.5 m0lkib1np;++lilx5 e suu8:i )i5 ghzn.
(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 constawvd 7vo tq z1jmrmo;fo;n+92 8nt 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 imo 1z+nwovr7oqf;m; td982 vj s the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes pol.e pn-jp5xk9v5hy )a int 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it -ve jkla5)xhp5 n9y.preach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches r;7ig1y as i 13amyiq4the 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 atwjc)rtu+x2 u5:krzksjr 7/l; tached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–sprjl /k2rkx)t+cwuu;jr 75 szr: ing system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontakcm ob iogd7/)3 ci9r.j 4mdj3l spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If c )3m d7. cj9 dgomi4iob/3jrkthe spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “g(ti 0*/fqq.w grrckh+ lider” (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 spee *q/ +kig. twhf0rcr(qd 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 takeojl43o/h7 8t1im d5gifsr*u u a 1750-W motor to lift a 315-kg piano to a sixth-story window 16.0 m ai3 7tjf/id54r* msoo18 uhglubove?    s

  If a car generates 18 hp whgk drv9exwaeat u 9/2z0f2+q8en traveling at a steady 88km/h what must be the average force exerted on the car due to friction and a2k ze9g92a/reta8 d wuf0 +vxqir resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What it0 f*4*/okk nj6kd8bih 2 gxmss the average power dk*ik bth04gx26ns*m8o k f/jdelivered by the engine?$\approx$    hp

  (a) Show that one British horsepowsgvrdh;(szk 99l ,(k7:npwkvq(n :arer$ \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 in i(qf6. f0-bwpe;ubsu1/z oskthe 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 herl,hna( /w2-gmvni /jg qbede +9-fjq2 1150-kg car slows down from to 65km/h in about 6.0 s on the level, jbhqvg a/ni +9j2n/q2fde -mge- wl( when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp mkly -ethxh12x7p1* z rez/y2 gotor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/st48v 1hv 5ad9)cqlq(2xsul qw If this motion takes 1.5 s, what adv4t5lwlu8(q 2xvq ch aqs )91verage power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. Wh9chiw3(05d t7l7u n8s)dmeeix4dzr7 g ; hzkhat output rating (watts) should tw7d 38ixh54h el 0k7s uc9 z;nht m(idg)r7zdehe pump motor have?    W

  During a workout, the football play g9dg77 oqj86.yqigzf pbrh v72*-srjers at State U. ran up the stadium stairs in 66 s. The stairs are 140qd69 og7 y7-r2gr jjz8sb. v7q*ihpfg 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 6.0 m6oy10qc t/s nk df08euh)a/k $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep a hill can itycezkts(fw20dp1 7,8pc /rkl climb at a constant speed of 75km/h if the frictional forces add up t,2z1try7sc/d(lfk ppc w 80e ko 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be 6y9lwhl0paw e5(c88puj9l rqtn l 8o5able to drag a 310-kg box along q phl9c5tao 80(u e l8r5jwln89wylp6a level floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts do 1u 5h8cu5hzp0 mb8gm2;w smhjsvm/: own 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 havepf/;)bqx p.hw 2+ni u ny)og;j built “5mi/h(8km/h) bumpers” that are designed to c; w hu go/nxi pjpyqb.2nf);)+ompress 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 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 ; ivt6i54vbkjdb;qf/t; .kojis 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cvbdoft4/.ji;kq j;5ki6tb; v m, 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 Owen sny6jcrie *j ;2:8nles’s famous long jump (Fig. 6–42) in the 1936 Olympics 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 a:y* rci;82nen6jjs el t launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without frictioen zn5q d/l2e9n along the looped track shown in Fig. 6–39 is to remain on the track at all times, even 5qndze92l/ e nat 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 hi6+rx2vb5x jtgf +x yf.s parachute opening. He landed in a snowbank, creating a 2fbvyjgfrt x +x.56x +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 whose02x hk7:h )/kopiel gz other end is fixed (Fig. 6–43):h/0 xgpi2)kk zo ehl7.
(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 3700os0rel0 u,2.d)(e +xkwi fdyt-m-high mountain. The climb is made in 5.0 h starting at retus,l0kwx ( fdoie 0d2)y +.an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevatorwh 3jpb5,krk el i76/i 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 claimsm) 6etkujt 1rl4jgd258lxoip -af1p, that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m 4ej,2fo)p i8 r1 xtml tak1d-g5lu6jp(vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and frg+vp xu )7;zralls vertically 81 m before striking the turbine blaxp ;+rguv) z7rdes. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical lofpilrph7fp)iaov /6 r5/+(b xop (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 speed is above the minimum needed, this answer doesn’t depend on the size of the lo7bf/(fi prorl5 pvapx6ih)+ /op or how fast you go through it.    mg

  (a) If the human body could convert a candy bar dire +/d d 49rtto ntmzw(6p2oafu06g*ndtctly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1000kJ) 2gtf*6 w+t/atz4 d6 d u9n trdnpm0(oo   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 upa(4+v83ud kwkun *zf yward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale comn(qu;tj0 )1)s d g n75phk8dvnyazav,presses 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 7vtn) gs05j8vkqn nd,1);puh(adayz does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a s2 fz ssgecu:.f v3o1r vd0tf+46r 6thlake (Fig. 6–45). He releases the rope when his velocity isd6furg 3vt6h:2zscr oet0+4s 1 s.fvf 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 distance of 5.0 m +o 4 ogm2swfi0in 9.0 s. What minimum power outpu+0oo ig2swmf4 t was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is: 69ut bsf1wiyirhb95 : 1bfjj pumped by reversible turbine pumps from a low to a high reservoir. To store the energy prsf:95t hb 6buiyj9ifj11wb: roduced 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 cut in half. What is the z 3 klb)+i1uq70kdalupw6f d0spring stiffness constant for each d fpuk60kiuq wz3a)+blld7 01 of the two resulting springs?   k

  A 6.0-kg block is pu.zwfcyv ;q0 fek8i8 h+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, how long wppgeve:xk572/mp v -cta5 efr6/i -qtill it take to accelerate from 55km/h to 75km/h Assume the :c pve27vfxie ak /qptpg--m5r5/ e6tpower stays the same, and neglect frictional losses.    s

  In a common test for cardiac dkck s5kv0,y.c 723yw c8lnmgfunction (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patien0ccsld k .7 8wv gm2nkcy3y5k,t 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 spewx4bn8(v1o juh h 4d-egs a 500-kg rock vertically upward a distance of 500 m, what was its velocity when it left the volcnb- du(e1gh4hx48vj o ano? $\approx$    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 offv ir;97m-:jpw cme; 0.p,jim(fv ep h 95kg/s (a) If this water wheel is set up to provide electricity output, what is its p7;i-r (e9epm .f:w mpm;jciv,vf0j hmaximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s