In what ways is the word “; ;::njlp vbomwork” as used in everyday language the same as that defined in physics? In wh;o; : :lnpbjmvat ways is it different? Give examples of both.

Can a centripetal force ever do work k)ybxpyz4 ,vh jpu n*:-on;w+tr, )udon an object? Explain.

Can the normal force on an object ever do wn1x:vovg1a0w1e 76h zq 9e/ kk4enhloork? Explain.

A woman swimming upstream is not moving with re6 wdo 27 9+vohzxl)gsvspect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done on ho)2 o7xgd9+lv hvsz 6wer?

Is the work done by kinetic friction forces alwa3tqr+6r4irb2m0 n hrqys negative? [Hint: Consider what happens to th6mb 04 +nrr23t qrhriqe dishes when you pull a tablecloth out from under them.]

Why is it tiring to push3 df*;n:maz7:n wsr snooti:) hard against a solid wall even though you are doing no naz ftsi:o) m;:os wnrnd7:*3work?

You have two springs that are identical except thaqq8zjiwh .35pk dfw*y4z+ h v2t spring l is stiffer than spri dz5i8h3v24w hqzqk+y jfw.*p ng 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 horizonto9iofmm 7hscgsscm*:jj -8f)06/u l gal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, ano:l60 g8c/)sosm 97j-msuc*fgi mfjhd 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 aw,/eacf 7lg. change when you jg/a. wea,lc 7fump as high as you can?

In Fig. 6–31, water bal+6 s,6njt zr 0sci2vbgloons are tossed from the roof of a building, all with the same speed but with di+rg, 6t06jb znsvci2sfferent launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h ab*)no0 .xtlh8 k(pfo qh2cvb7dove 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 qp8v2h7(n* fxcdt0oo)k h. lbthe trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests uprg e j0 t7tmhz2ho:c6.n) /r::tdl wtmnight on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Exw o). hhz t6nj:edm2/cg7rlnt0t::mt plain, using the law of conservation of energy.

A bowling ball is hung f13okrtuqk d8n +j ,w2from 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 toow8dfnrk1uq tk 2+3 j, release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top of a wv*)w e, l-qrshaterfall falls to the pwel)hs vr* q,-ool below?

Describe the energy tranyncw ca9r(tk6 s6;a/gsformations when a child hops around on a pogo stick.

Describe the energy transformations that ta gar9lll6o*m1jjc-;f ke place when a skier starts skiing down a hill, but after a time is oj;-9l* cl 1jmfglra6brought to rest by striking a snowdrift.

A child on a sled (total masj8(uev u 7 lqa2ma3 oqi..x2zns m) starts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no fr8ieqzx3 na.2m l2q.vjuauo( 7iction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen4o;gzrfq1 ip4glj/qwz ) zqyl+o 39e8 log in their path rather than stepping on top and eygqq9) 1z+fzli rw38joogz l4q; 4p/jumping down on the other side. Explain.

Two identical arrows, one with-nna9,utoyacv dp 3,5xfk ym:3 so69t twice the speed of the other, are fired into a bale of hay. Assuminx 9tucdy6 3fovkn :,9m yapaont3,s-5g 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 simple swinging pendnsb-s6od m7v7t1exh i 4se7(c 8ho uh*ulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandxmo4*ssv1dn78c - us6tb7 (heei hh7ofather clock has to be wound up.

When a “superball” is dropped, can it rebound to a heigh yfxmhxd6zx8 23jk6f)t greater than its originxyh86fx) zmdf6xj 2 k3al height? Explain.

Suppose you lift a suowp 9d3o8m z9j1 srg8(2o pidnxly)t4itcase from the floor to 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) the time it takes, (c) the height of the table, and (d) the weight zo8op9 )l9txrw3 d gon1 sy m(dj82p4iof the suitcase?

Repeat Question 22 for the power needed rather than the wo+uc+47ggq+gu y . lbburk.

Why is it easier to climb a mountain via a zig aif 7my lopzyl:907i4zag trail than to climb straight up?y apo9z :fy77l ii04lm

Recall from Chapter 4, Example 4–14, that yogg v4zv ax+a/ejn)f59 u can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raisee/x5+ggv f4a az9j)nvd, 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 dlk kbal6,yz3af 9s+z2mc-7m m river falls 2.sm7-m 6fml9,c2la by zk3 k+az80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m 7 j2tqy,mqoc/govf 60 high. How much work is requ2gf /ojt 6m, qc0q7vyoired?    J

  A 1300-N crate rests on the floor. How much work is required to move it at conq5 b)cvm.p q9hstant speed (a) 4.0 m along the pq)h.vbmcq95floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crate 10.3: :xquihz ji* njz2;h3 m across a rough floor without h*:j ;in zzij2:3quxhacceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kglle09/1 :rr;sv r:+kic tawzp is accelerated by a force across a floor at a rate of for 7.0 s. Find the net work done on the box. ts0::v re /lpir w9cr1k +az;l  J

  Eight books, each 4.3 cm thick with mass 1.7 kgezu np 8qko62f +ll53w, lie flat on a table. How much woelz2 5polq k6n +38ufwrk is required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to ak.stqholfx (,: x6m, liff objects we might not otherwise be able to liff. Show that the ratio of outxl: 6ofxt ,kq.(,smahput 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° in./z*wd-py/ ftrhd52sm m4x ltcline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calcula w shf-tzl/xt.2 /5 drpmy*4mdte:
(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 acceleration ayr r 8 ikmq4737uts-tof 0.10 g upwar-k734s atm uitrr y8q7d.    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 axis9han/j +f70ewv3m(q a,n bmpl is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shown in Fzp qjbd k1uyzy8fg96y-d+ h :3ig. 6–37. Determine the work done by this force to move the object (a) from x=0 m tju386hd +bz-pdykf1 yyqg:z9o 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 iymh( afmxq6wgs(cz p 68 6lae7qq*fs-454oob n 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 oxygydc 8 ml/s;g*fj*,a4q p+k bm xoq2d3len 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 speedte2hi6z1z 1re/ e h,ul increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required tobiev7p w 5q2flvmc72wi +)hl3 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 bobu,u o5a. +zhg6upr2 e 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 sm pb :.h68r7xpwjhw7exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as hx7mbp .6:78 phw rjwsit leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielde /n3;g p gcfazivk3k-*l.4j xyr’s glove backward 25 cm when the ball is caught. What was the average;x.ji vnf lgz3/3gkc*y4-ap k force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will a3roe:xw93 v,tqe sa8 its minimum braking distance83oa:wav q3,e 9strxe be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road,e l* ek/ngc*+w investigators measure a car’s skid mark to be 88 m *we*/ nglkec +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 mass not matter?)    m/s

  A softball having a mass of 22g9gmd1 ;;hiagf 7btryo3pf 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglef2b9 dira2f;17tgg g ymh o3p;cting 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 byj4l :nrey +i+v someone who does 80.0 J of work on it? Neglect air nvej+:4 +lyri resistance.    m

  A 285-kg load is lifted 22.0 m vertically with ;o xjem:sjlr2u1 x+x/ q)rrw7an acceleration by a single cable. Determino7+u:w rq 2exjsx;lj 1)mrx r/e
(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 stiffnessqjnq06;ggzyun. 0t )q constant, k, of 440N/m How much must this spring be stretched to store 25 J of potential enerq )q0 tzg g6nuq;y.0njgy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. Whhh,toi4k+d xkw0l6m, at is the change in pot ,w 6mdxh,iol 4kk+t0hential energy?    J

  By how much does the gravitational potential energy of a 64-kg 6vfaz+05c )hp8fpu6o/k -djyg xe0o spole vaulter change if his center of mpp hfax5d0seuoz/-kcf gvyo608)6 +j ass 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 sbx3d5o;bd. +otmi f:q trikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. Whatq :of.m3ob5i xb+;ddt is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m p.ij wt)( tu7zuiow5 5/rgx1 yabove (xyiug/j 5 7t)i .r uwzw1po5tthe ground. What 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 climbs to the tcw 55,k)d4hseb ysc1 iop of a 3300-m pea4s,5w bye ics15)hkdck.
(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 e3 (0t0r2vmpql/ yp zc: lbwz,d bi-fy5nd of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg maq z-t zmc,rblb(325/iv0w:p0lyd pf yss 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 atzbq5it33.xp a top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high canaz i3t5xq.3pb she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, x hd4mjd4((;ebsltf8d)by j9 slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frictionlyq1c /9+c++ y v/pdtw,pgakkbess 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitational pot)6f+o9t ye f4+7x3acy8y duzwf0x bgqential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lif+w b+4x9yyofg0z73 f8)d utfceq6axy t 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 from the top of a platit0hvg9br1j*o0u9enn9w pl + form with a speed1o*e0w9 v i r+nhjng0t9lp9ub 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 - yi 2;i8hto.efe ns ah3no:9 c3mhwu.its mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 ei3no3 i. yf 9we :th.c8 s;2o-numhham. (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 without friction along the loop*3a h0-+z- sb:fzopn(ysrlpj ed 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), fp0 -a *j( :l-3yshpf onszrzb+rom what minimum height h must it be released?    r

A block of mass m is attached to the end of a sp6 hcjemt(*l l*ini;b.ring (spring stiffness constant k), Fig. 6–40. The block is givl tb .jm;h(elcni*6 *ien an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord whose un:rmq 91jm nj53bb+w/m+ruf7 vstx u 6lstretchedl:/1 u+3rw 6fun9q+b vxmjmjm t br75s 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 dyk :x;c :bfw4iragged up to point 1 where it is re::x k;y4icbwfleased from rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s attu-y dbyvus.qf*w*6c/hgw(: 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 botto)((awd:5dm xyfau3 rabg5: g.jtvqbmb05i :o m 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 b(b btxj:50.gau5ri yafv a3 mdom(b5wqd ): g:rought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle upsf)p+b b3nm,x,t ti*q6nov q; 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;2k* bdc.wjp/xzx 99r) czcjk mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How muczc2xkcj p z.9bjkd *;x/rc9 w)h thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom with drmx , b;cpf26a speed of 2.2m/sxbd,mpc2 f; r6 How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides down 6g d9,jcab1h43i ppthn 7qxq 5a 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 treb a7s jq-3z8orieqq/wuo3.v q-h1) gae 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 :q* tsdgo8nlg18 .omty63sfxheight of 2.0 m, and it bounces back to a height of 1.5 moxm6l1y.s tf 8to:s3* gd8ngq .
(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 fb nfl h)-;rju3m2pl3nloor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction ih 3;rum-lp23ln)f jnbs 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Figo uic/o.h54 qtq.ya0p. 6–41 passes point 1 with a speed of If the average force of friction is equal to ooqou .t.5y/0p ihq4ca ne-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the ,fjsqi32iifvupbbe e i ,*d 5f vh*4wl(:8*vpfoot 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 horig;t)gt12 jdec e j zeo1nq2(+szontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–n1+gg)c; et1ozej2s2j e(tq dspring 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 vu3re u;)44fra7ubsn mery light horizontal 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 se 7u4rru34u )am;nsf bpring 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 shuttle used a “glider” (mass of 980 kg includowd5 c qbnnz0p09pe46 ing 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 absence of aiz 5nwope4n pd0cq6b 90r 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-story w 3kqi*e l(9rxzindow 16.(liq9*er x3 zk0 m above?    s

  If a car generates 18 hp when truv 6cwgq9o ;u.aveling at a steady 88km/h what must be the average force exerted on the car duewvuc6.u ;9o qg to friction and air resistance?    N

  A 1400-kg sports car acce cb1,1 9:ajtutj7u2vtu up x2alerates from rest to 95km/h in 7.4 s. What is the average power delivered by thejatauc9u:uut72 v1 t j1b2x ,p engine?$\approx$    hp

  (a) Show that one British horsepo c(smk8aqmg() wer$ \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 the form of “kil00uaz b jrqwn1a-fg: :owatt-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 p )/ yvto umh4-ys5(hi to 65km/h in about 6.0 s on the level when it is in neutral. A (st)ou/4yvphmy -h5i pproximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in0lp ,((p p.z-c6 t6 klnubgzfd 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot f)fypzccup- :8n8d 5hs-tik,z rom rest to 14m/s If this motion takes 1.5 s, what average id5 pk hcpz8-ycu tn:,- fs8z)power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. Whalx -+gt s ja4/hy0kxz+t output rating (watts) should the gt y4lhz+ -xj/0s k+axpump motor have?    W

  During a workout, the football players at State U. ran up the stadium sgni16y,v n 2/a0gus lotairs in 66 s. The stairs are 140 m long and inclined ayn6/nasi1vgg0 2 ,luo t 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 6.0gq4 x fp1:-p.+-jps+oar b3t zc: yqor $^{\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 mrrnri o,/3oy+8de.bn q1i n p9aximum power output of 120 hp. How steep a hill can it climb at a constant speed of o/3.o dbir,nre+9i8nr y pn1q75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motbuc k5; 0wr9:-povfay0 s sl5aor have to be able to drag a 310-kg box along a level floor at a speed oy;5 sr-uobk0af9 5apl s0 wvc:f 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dow 3 6 bjrgwrp/aclg(3;xn a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpervyyoz ;8pitt0 v;+7u hs” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective sprihoyziu 8yp0;+7t vt v;ng 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, and tlaka8(nttc wb)5v f,7gtm. 8o he remaininggawak8(8vl om.,c7 b5 )ntft t four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Oly 6o*sbtqwtl6.mpics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he nb6lt.qt wos* 6eed at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding withoui:hu uk 1a)z80q7ebrct friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very to:ecq a )h70ubr81zu kip 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 37bwltbah8koj6-j/ 8 x30 m after jumping from an aircraft without his parachute opening. He landed in a sn/j lwjb8-6b8hkat3x oowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L who,wpbts xr)+s1ub ni(y+:au7x se other end is fixed (Fig.ristbxub: xpwsay,u7n1 +()+ 6–43).
(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 wolfa3uo3w o bl-vz(zfl8;/ 4top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Cuo(3/l; lwlvbawf z 43oo8z-falculate
(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 elevatork9qih vp95g9x8i8txq b qal(9 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 pe tz59 vjadns -gk/)nby +s0-daople per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power nees dsank n0ay9/5j+gzdbt-v -) ded.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vx, pomnztx i */j:t0-ws.t /sr ikmf;5ertically 81 m before striking the turbine blades. Calcuow 0itmn 5zi,.:s/xs-/k *jmfp;ttx rlate
(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), thw8afkpx3 ku/;e 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 a8xku3p wk/f ;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 bauj u*f pu(b,hii 9y8k;twa2l2 r directly into work, how high could an 82-kg manjuiw ,; 9i t y(hlfk8b2p*au2u climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an (qbk)fm7m-ju *p1jjzupward 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 bathroo;k.02lwoa 8xpfh(n mkb*oh,vm scale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale rk(8 . fowkh ;*mha2lvnpbx0o,ead at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a laked9u,ohm4dv:cgs5mjc g8 e 0+j (Fig. 6–45). He releases the dsd9+ 4j0 8gm hv5c,gjuoc:em 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 w 8+ saa-j-o2s5tvj-p (qiqtaa vertical distance of 5.0 m in 9.0 s. What minimum power output was use2qt 8q--a5t-aa(poji sw+ jvsd to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water i8ljmpjrnd, ox- i8r9-s pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MWlx--p imo dr9r8 8,jnj ($120\times10^{6}$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 s4dp+ .gjkz7ytb5yt s5pring stiffness constant for each of the two res.+ y45bdpz 5s7tg jkytulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rougr 5 vhuu -eif0nwv,w67h 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/h8zbk k/d -s r91oqn )d(-ag9u5ycq zgp in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the po 8qqy/s )5g-pg1r bc( uzz-9akodkn9dwer stays the same, and neglect frictional losses.    s

  In a common test for cardiac functe72q3j7( :k/wduw we 0nzxoirion (the “stress test”), the patient walks on an incenw 7doq3/ rke: 7w jiuzx20w(lined treadmill (Fig. 6–46). Estimate the power required 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 5c8omxs m20ae in5.; o jgor8hupward a distance of 500 m, what was its velocity when i.si8go r55h2mm x08oeo c;jant 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 ofhs yd6egosr j3 +1p 8bc;bl+.z 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its max eh1 o 6lg+rdby bz.+pc8;js3simum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s