In what ways is the word ox/kew/ 0c iv7os3q-a “work” as used in everyday language the same as that defined in physics? In what ways is it different? Give-o/io/ws7xvcq k 03ea examples of both.

Can a centripetal force ever do wr-rbp. afhow50 lok14 plple i6szm :)bft,;3ork on an object? Explain.

Can the normal forcec3c;jvdv bez,,gqssp128 m ;q on an object ever do work? Explain.

A woman swimming upstream is not moving with respo+goke6pvz3+2op js8 ect to the shore. Is she doing any work? If she stops swim6+o +opkvepozj 83s2 gming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consider9bxz u4:heheanj; ,*m what happens to the dishes when bu,*zhjexn;9am e h:4you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you,d;5fv(mlnh,lkg 76xxj6zsy are doing no wor, n, hdm xvx 7;(lzs5kg6yf6jlk?

You have two springs that are identical except that gyc;n ij.1t5 fspring l is stiffer than spr jnifc1t; .5yging 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 horizon/atp6 oqht2 *smx 3yq5tal force on a block that is free to slide on a frictionless surface (Fig.6-30). Th s62my/px*qqa o3 t5hte 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 you 1gk-(dkfte6gsa j,,c er s0d9r gravitational potential energy change when you jump as high agd,69e kr, edcs-0 s fk1a(tjgs you can?

In Fig. 6–31, water balloons are tossed from the roof of a kc zqg e380xt7building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistanc0ectqk738 zg xe.

A pendulum is launched from a point that is a height h abovlj2i975tvrrl e its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum isilvr2j7 t9r5 l given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compreskpjg q*lmgfe;,) 9me6s the spring by pressing down with you gqpl*gj 96f)km,me; er hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung fl/b1qza 9v .alrom the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. W.1lqv az/ab9lhy?

What happens to the gravith.tto rqke41x sz63lu s g,)9.v wa)gzational potential energy when water at the top of a waterfall falls to the pooltgl s w4zk)er v6az)x ,sq.t9u3h1go . below?

Describe the energy transformations when a child hops around on735zea xxc aos7uiwt,+.ce 7i a pogo stick.

Describe the energy transformations stry*s13 +nz jnwn2f. that take place when a skier starts skiing dowr23 fy1njtw+* zn.nssn a hill, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of2lb)2 3goquu + d6zfzf a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) ifzuzbl22q)fd+ 63g u ot is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in theok7) 4bk *i2up gkyk*oir path rather than stepping on top and jumping down y2i )b4*opo7ku * gkkkon the other side. Explain.

Two identical arrows, oncvar2w7 1jfwg1s:r u8dr0 /xtmc/gi9 e with twice the speed of the other, are fired into a bale of hay. Assuminga x cg/9m1: srr/d wugivwr07jt8c1 f2 the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a s1 m8lbdod 0:isimple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking frictsddo b10l:im 8ion into account. Explain why a grandfather clock has to be wound up.

When a “superball” isr 26wc rvx*es:yz0.c q dropped, can it rebound to a height greater than its original height? .s*0 cy 2veqrcz6xr: wExplain.

Suppose you lift a sui. 67vbm ko+d8gho yhs1tcase from the floor to a table. The work you do on the suitcase depends on which of the following: oh6gh8k.71ysovb +d m(a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 forsvq0;o0gsxmaoc g7xg 4j- )r 9 the power needed rather than the work.

Why is it easier to climb a mountain via a zigzag trai f*1q ddkdp,r; n0wm,bl than to climb straight up pnfmd,01qkd,;d*bw r ?

Recall from Chapter 4, Example 4–14, that you can use a pulley and g (oy- *,z 8pymjceu:2 7qq*fdmjun e8ropes to decrease the force needed to raise a heavy load (see :7ecjumyq8-j (,u of* d m2yzpqneg*8Fig. 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 p1.m (wnkj.f s* lyerls/p3kt. ile driver falls 2lk l*wj.(.mtrf p3yes.ksn /1.80 m?    J

  A 65.0-kg firefighter32ng7rij*i zec8oyl7 jfj, 0 d climbs a flight of stairs 20.0 m high. How much work is reog0yldeiz2 cj77j r38f*ij,n quired?    J

  A 1300-N crate rests on the floor. How much work :cz aceana; k5q;l8:k is required to move it at constant speed ( aanzqae8c;lk5k:c :;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 dtq +9g3e/uc )w/ scca(moa;j-kg crate 10.3 m across a rough floor without acceleration, if the effective c jd3stc;c//aemc a9)qw(+o u goefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a forcery-o se5w5 u2k across a floor at a rate of for 7.0 s. Find the net work douyrk2 wo- 5se5ne on the box.   J

  Eight books, each 4.3 cm thick with m1f+ w*kigoi5 kdfh68 w h3cj+kass 1.7 kg, lie flat on a table. How much wor hg85h+k1dk+jo6*f k3w cwfii k is required to stack them one on top of another?    J

A lever such as that shvfrlp3 e;r-evh- bz1e3 +o7djown in Fig. 6-35 can be used to liff objects we might not othe +o 3p fehje-1l-v3rvz7r;dberwise 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 down a 28° incline and is kept from anq : lx(0,xykw.uffw-ccelerating 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. Calcux :(w,-n fulwyf.0xqk late:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M an mt7ot :4,ymkv45eoecb v ,vf. acceleration of 0.10v.4mbovvtymk 4fe5e c7,:t,o g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance axis c:fvqtxzq-c8 u, la(xurxi(7s .1vrdn- yn36 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 fkrczv qf se4*d2d5.) along the x axis, varies as shown in Fig. 6–37. Determine thee24 rdfdcv.5 qzfks* ) 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 pame hc bs7.x36yrticle 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, awv/ pa+5 jfp9egd* c9 +tsoin9n oxygen 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 increap3qgdd )p5hos +g(d+q sed? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required t t q)db tgfrjw9q6:.n2o 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 1qq./x*zwe qmg6(n j :dz z:0cc05km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts agstc:l;n*py7sd v;t)x4 7hse n average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?sstgpvt77;h e yn )xc*ls4;d:    m/s

  A baseball (m=140kg)aa)b(so-str 2d lnp5k9t nu5 ru-nvbg*ge4 .5 traveling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. Wh9 t-5uoalgutv.epb ra2 n* rd5 bn4gss5(-nk)at was the average force exerted by the ball on the glove?    N

If the speed of a car is incrsopbb o2i: f )8pr6dt;eased by 50%, by what factor will its minimum braking distance be increased, assumibtp2s; bdf o6o:)8 rping all else is the same? Ignore the driver’s reaction time.

  At an accident scene on fj-5c (9oy(vjis wdb9a level road, investigators 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 speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mbv fdyoij9j s9w5((c- ass not matter?)    m/s

  A softball having a mass ofcg,c om2sg331 tc8)ttsd w-ho 0.25 kg 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 during3whog)s, 8d tt1ocg sc2mtc 3- 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 upb -jz1z4s74vokms8 9hxt ck:l by someone who does 80.0 J of worb:hkm8 9tzkolv1 z4s scx4 j-7k on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0ts6b5lrttcuz/2 8 /xf m vertically with an acceleration by a single cable. Deutr6txct/2bf 8/z s l5termine
(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 )l81wzf sx.ea ); jdsoconstant, k, of 440N/m How much must this spring be stretched to store 25s1;l w8je saxf.)d z)o J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is the chaz4*apmlhqagqo:cx. iq * wq:. -zo*:w nge in pot: pqqm .*qwlzh *g. 4wzio-:o aa*:xqcential energy?    J

  By how much does the gravitational potential energy of a t+;o7)xz ent a5c4jcbg/l bg 764-kg pole vaulter change if his center of mass ri7t+)c/g4jtz ax conbb7e g5l;ses about 4.0 m during the jump?    J

  A 1200-kg car rolling ons9-otq vezb /i l5 7zwbbk38s+ a horizontal surface has speed v = 65 km/h when it strikes a horizontal coiled sprio5+szlvkizt-e7b 9b/ 8s3qb w ng 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 ;acze*nlj 2 ic*c:yk4lifts a 2.10-kg book from the ground so it is 2.20 m above the ground. What is the pote*cyzck c24ne *laj; i:ntial 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 climbs to the top of a 33.*hwqdgpez9i )pbn82/ olgu400-m /9wpole gn)u qg2b4p.8 hzid*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 rullzg d1clrnt qi)*0f h477p:kq;p 4 ffqgt :;acer. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with tf;; tzl*q n k:ligpq:1q40apdc7h gfr c7)f4the ruler marks?    cm

  Jane, looking for Tardwds lh ktxl 5r,nlg(qb -4(7lsp3(1xzan, is running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can shpb((hlsw-xgln1d3 x7k ls4 (5,t qdr le 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 frirg9evd0(m-hgmb .f. gctionless 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 upu:j40g twkdzz8d(ee0kb b0v8 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 kicl ui 3ia57wvp x)yc.1netic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the grouy.wc1p i)7a35ucxi vl nd in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward fpjfn5 zt7 8ju3gwjw- .rom the top of a platform with a gnzw-j5uj78.fj w3 p tspeed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose bv1r5mm. u+re spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it givbveur.mm+5 r 1e 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 withoutee k:3 dazf,u( friction along the looped track shown in Fig. 6–39. If the block is to remain on thee f :dkz,(3aeu 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 th /)s)iyus3* bmym kyc:l+ri3i e end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial displac3/) i3ys yi+iy:k) mu*lrms cbement $x_0$ 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 j:da im64zr4-s6bn(zqvt f 1hmumps from a bridge. She is tied to a bungee cord whose unstretched lb -zh smtia(166rvfzq 4nm:4dength 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 to point 1 waar3cgm1m 5 1rhere it is released from rest. Assuming no friction, calculate the speed at pog1r1 3ma5marcints
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(fgxq g(sbk14-nd msn,8t .ts pa/6wx 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 bottoc)kzl(wo4 p ns5bp /i;m of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spriniwn)z;(p4op/ lcs 5bkg, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle lvc s7 s xan:oi50)nb 4cb4(tzm-dcu;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 w75 e2duh-wqx mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collxe2u7dwh- 5q wision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the botcvmrq, x32l );5( bgszt5t; bn9 lcgdctom with a speed of 2.2mx smq,cl9 ;t)cg (bz53v2dn5rt; blcg/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides down a-t/ml8y f3 fwf 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 asu y9 +8bepv0 5etiddw,/syw2 tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a height of 1e 9k0,d1mlq8 f+ +xcoqntlf8 d.5 m,o 8qm+de9ct1fl+nf8dlxk0q.
(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, ishty ivvp.x,nm 9ubxl(4t 1 +a- 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 coefficieb9i .p(t4 hn1 ya muv-,vxlx+tnt 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 witho 1(q 8awb, vies(jtl; a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled ijltsiq,8w( ( 1ave;obs 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches/ya0 gp::otep 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 +j i4d /cz4y+ae3o*4c itznneto a very light horizontal 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 c4y* zzid+in4oean4c 3 c/je+tm 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 at .)oqvnh :jv q8kmxbhj(k0:)ktached to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of frictio 8hnk)kmoqhxb(:) vk. j:v0 jqn 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 shuttp) bp;is7-t +p nzyor-le 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 -pr) -bzi; n7popsyt+ been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-s 5bz;uq tw8gf,sc -* 2w c*nmf.heq.fwtory window 16.0 m a ff;bz .2*qu ce5fgw.s-ncwhw,qtm8*bove?    s

  If a car generates 18 hp when traveling aryal59k:*wm8 g v mes4t a steady 88km/h what must be the average force exerted on the car darg4*yv wseml8:k5 9m ue to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is t4q l+eigh tjei( 4tn 5b-kk*l0he average power delivered by the ehktg(+4i *4jlqlk nie-0 b 5tengine?$\approx$    hp

  (a) Show that one Brit+czi lkp +mv6i(dw mh: s8,lf:ish 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 in 61 fo7rni c4hemv;e:s 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 0i 7sklrfb2a(6 yn+avslows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (wavy7lbk 2r 6ias+0fa(ntts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 tr2 uvq2b3spryb- y7. h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from restq(lgw2*80 3* yhyzkm7trgd et to 14m/s If this motion takes 1.5khtdye7 y tl*308*(qg 2zrgwm s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a heightm06 5c 1v-f4q,xeld vzvewiz- of 3.60 m. What out5xzm0 vz,dic 6evqve--l f41wput rating (watts) should the pump motor have?    W

  During a workout, the footvf :xu**jpn1 rball players at State U. ran up the stadium stairs in 66 s. The stairs are 140 mj*n*1p vux:f r 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 cliaax;nx54o8b csir; y h/(.vi mmb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep a l eiqv9a(w 6j1 s6y1uehill can it climb at a constant speed of 75km/h if the frictional forces adj 9e1e(ya6qiw16u svld up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to dragdrk7v- o1vw4uzedt(5 kx.2pjuz/ rw3 a 310-kg box along a level floor at a speed of 1.2m/s if the co7dwkr o e15p jztwrv/(v zxu-.3du k24efficient of friction is 0.45?    hp

  A bicyclist coasts down ps 7asjj.lzf*)0 mey *a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/ hj0 2es syfazd *bp0w46dco*5h) bumpers” that are designed to compr* ds6 c*dwo0 2es4hy5fabj0p zess 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 is 10.0 cm off the ground, andgnwqxa(1qsl/lc8 +xo.h.d ) n 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 toa nlh 1lqxg( o8sc. dqwxn+.)/ 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 19368a nlbsd92t,f6d ys6o: xwrjp pe+))f Olympics shows that his r+s )d s,fae6opw9dx:ynb6pt)f2jl 8 center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding withou3fiz(xgg /0rjm+fr l) t friction 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(rxgf)/lf3 ijrgz +m 0 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 hkd9 fm:x4y*mb is parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimatem dfbxy *:49mk
(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 lengh5 .r q1*meiq-4oqanzth L whose other end is fixed (Fig. 6–43)hn i.q1eo4za q -qrm5*.
(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 t-4 tr3j2o8 nhlnbbw6mountain. The climb is made in 5.0 h starting aor63lt nb-hjnw 2 t8b4t 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 breateq 8pf.tj1s 5p/l3gzz+m 4m pks when a 920-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 qxno3j7dz qk* j p+14pits lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate thdon jj +1xk4ppzq* 37qe power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls v nscz.r5r* j+aertically 81 m before striking the turbine blades. Cj c5rz* ars+.nalculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. 6–44), 2 tta ;e)qodt,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 loop or how fast you go throa) ;tto t2edq,ugh it.    mg

  (a) If the human body could convert a candy bar directly into work, how high c5h 2-i*3b8 u ekozfj+natcw 6uould an 82-kg man climb a ladder if he weuf3k2bozju6ie+ h*a-5 8nw ctre 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 angle o5ld1w :eq y6wthd:j;cf 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, cog/ g0dqyg9 z87l oxt(o6:bithe spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scq9g7gzb6t gyl: 0od (oxi 8o/cale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runsh:,hw2*0aj8uk* ue ws xvzvdu-jk . 0u;ij8eb at 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is zero. ej 0,b **uxw.;k8sjejh0av2hku dvw zuu8i: -
(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 dist t 9 (.)9hf+dx;6izi6 .6ncwatnj3jaaf lxlneance of 5.0 m in 9.0 s. What minimum power output was used to a;a6fi+ c nd a.lh.tij lxn9we 6(n)3j6faxzt9ccomplish this feat?    W

  Some electric-power companies use water to sto8ej:lym nlz 2q di26m1c4 5sb,u.nvp xre energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produ 2m, zmix qyudj:sl2l8e.b16p5 n4c nvced 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 thet3)gw6wyn :wnd wb13coub0 m( spring stiffness constant for each of the two resuloc: w1y(g3 w)bmubd6n0nw t3wting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 37 jhr,4elcd5eo jx* g. ($^{\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 tq( 6qr+siydkw(w, 7bsvp4g. 3.2 s, how long will it take to accelerate fq.skb 6q v(rw gy+d(7sw4pti,rom 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the paqc* g zrb knq;df4v/-2tient walks on an inclined treadmill (Fig. 6–46). Estimate the power redfkcrv 4-2*;qgb /znqquired from a 75-kg patient 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 50 iqnc/3ok h)ny0gc6 t*0 m, what was its velocity when i* )/nn0qt3okcychi6 g t 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 fro*qjs s 5s7dp.xm a height 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 maximum powx5s7 *ss.qjdper output?    W
(b) What is the speed of the water as it hits the wheel?    m/s