In what ways is the word “work” as used in 2x;)2hwbwb.hj m3ayx everyday language the same as that defined in physics? In what wa y)m .3xxbhwwh2ba;2jys is it different? Give examples of both.

Can a centripetal force ever do work on an object? Explais b*5gb qor*awe3bq( tx /cz kuqd7:7)n.

Can the normal force on an object ever do work? Expdq7 9i/q 90dmo 6zxqzf6n.vu hlain.

A woman swimming upstream is not moving with respect to the shore.,+qa7 4v hnk5dfi x+rz Is she doing any work? If she stops swim,a4x h zdnq+7r5vfki+ ming and merely floats, is work done on her?

Is the work done by kitg s28rz j5;ns2apxr:netic friction forces always negative? [Hint: Consider what happens to the rp 22gjnt5x;sa rz:8sdishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even 7yt fumi1ri5e4 xy7 t8mw ;2iethough you are doing no work?t2twe;yi 1 y5e mx77i irm4f8u

You have two springs that arhqqhqu-kny5y 9me8; 8 e identical except that spring l is stiffer than spring 2 keh8nuhqyqq98 y;-m5 $(k_1>k_2).$ 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 c dm2i6q hw5(d2 gao4cis free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the tim q6 cd4h (i5md2gcwoa2e 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 gravitat8jvwgcp e90c) ional potential energy change when you jump as high as you c g8)90 cvcpejwan?

In Fig. 6–31, water balloons are tossed from the roof of a building, all withz*qk 7qbz79 ng the same speed but with different launch angles. Which one has the highestnb qz9zq77g k* speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h ag 8 m+u82ou2 c;a6dis; vcg;z;lndnxmbove 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 mci+zu2ov d m6;c ;s8na;28xnd;uglgalong the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass bi*ol) p b9+ d5v0tgjhm rests upright on a table. If you compress the spring by pressing down with your hand and th0dtjibl ob 9+p) g5h*ven release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from kik ;0vgoa x/jo2)jp+ the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball kpxg2j/o+ij0)ak;ov 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. Why?

What happens to the gravitational potxrxmx+ vktffi8o0 9 b)4 f)a(dential energy when water at the top of a waterfall falls to the rx a)+)bxd4f0(imf8v tf9kxopool below?

Describe the energy transformationq3; 4ud9h 22 :twlfni(gquyiis when a child hops around on a pogo stick.

Describe the energy transformations that take place whenan3 j aq2eg0es9o g97*k/vfsh eq9+ gr a skier starts skiing down a hill, but after a time is brought to rest be+ aefshneg o39*g20a q7vs jr/g99 qky striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hm w lk8 rhhm,wx-:77tbill 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 friction, and (b) th-8 :bhxwl7r ,tkm7hm were is friction (deep snow)?

Seasoned hikers prefer to stepv (mps(e yz v3t/o;fji*y1k jf/vwt19 over a fallen log in their path rather than stepping on top and jumping down on the other side. E yf t1/pi(;j v1 mzfwvvk*9(3yj/ tsoexplain.

Two identical arrows, one with twice the *9)xob91 jvvsihd dz. kli3r4 speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow w9i4z9x.v1 bkds*)vi3 rhl ojd ill penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a s *u-x3 g6kxgmtwoz8-n imple swinging pendulum in terms of energy, (a) ignoring friction, and (-xxungwto3*k-8 m6 z gb) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a h,r;( k9j:sawl3un j zh.ps0nyc7wx*height greater than its original height? Explain , xnzw s0uyn j9kh l3sj7acr*.(;p:hw.

Suppose you lift a suitcase from the floor to a table. The0gd mqt, 4*ffp work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated ppfft q 0,gd4*math, (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 rat5a zu 6.j dc.c cd3;6xn dpfry/zh9ie6her than the work.

Why is it easier to climb a mountain via a zigz386i ;nqr: .xwris2lvbqv/ yf ag trail than to climb straight uv/inrbvi; x3lqf y 2r6: swq.8p?

Recall from Chapter 4zp1hd w6 ;tpivk/xz; ;2zgdu + s:.nrd, Example 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, s prz;t.dgduwn;z 6 2h/zx1;:k ipv +dhow much rope must be pulled up? Account for this, using energy concepts.

  How much work is done byt 5et6yg+0uxt eni-w5 the gravitational force when a 265-kg pile driver falls y- xngti65tew+ 0 teu52.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 umkk-sz(l(3 qwet ( .nz6q5g jm high. How much work is requiredk5.6wj tzq(( ug(-msz3lkqne ?    J

  A 1300-N crate rests on the f-m8 d*tlct4 p+ /tmq/lz 7dufdloor. How much work is required to move it at constant speed (a) 4.0 m along the fl4zt dt c/7m+ ftdl8um/d q-p*loor 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 crl)f8 bv,t3bo ::ix fbcate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was 0oc ib3bbv8f t )f,:lx:.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate of ft,l2 tktvh6 3jp,(k.zk xei(m or 7.0,k .h3kp26xzjvtl t (t, mi(ek s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg,ul;/k,stl y6u0+r aa nb n1iqw.8 6bqrmh:)sc lie flat on a table. How much work is required to stack them one tnawm +sl)q8ais;cn l0 bh6uq r1/:.y6urb, kon top of another?    J

A lever such as that shown in Fig. 6-35 can be usb/l73 tflh b/ g3hzn)ped to liff objects we might not otherwise be able to liff. Show that3 /pl7ghn/ bzfbl 3h)t 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 ed d)u7rj ok sqzb;5).m down a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). )kde. )o ;5zdbjr sq7uThe 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 helicopter of mass M an acce.j (iolz0x n ,ged8gm9leration of 0.10 g upg,(d8 znjlmxg .e09oiward.    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 a,q ib0u4xh5 goj/qo 2xnd 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, act; ;n :xppuptn;l;oi9o ing along the x axis, varies as shown in Fig. 6–37. Determine the work donei; o;n l9; pupo:;nptx 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 actqli)gf4/+nvgqm)ioty69f o 2 s in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen moleculeo zfun r+2*dup;t +xw.a)io0f, 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 factoxro4 :sxxx3d*r 6 foo::js ;ev:;cmybr has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an73,m5qtv pope y35vy w 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 tp u 9j)xpn /-jy/gx.djraveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired7l.c 3w/wn vgh3+hrxn from a bow whose string exerts an average force of 110 N on the arrow over a distancexn +.hw/3 cg7vh3nrl w of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder0n/a yawa0rn 6ym* )p7vpr4nr. bmk*x’s glove backward 25 cm when the ball is caught. What was the average force ex)wrn 4 am r7*p mannxa.yr/0ky6b *pv0erted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its m,n.nqia: w v1hinimum braking distance be increased, assuming all else is the same? Ignore the driv:v nnaqi,.h1 wer’s reaction time.

  At an accident scene on a level road, in*f5cn w8mznm e6u (:vxvestigators measure a car’s skid mark to be 88 m long. The accident occu8vm:6en fc(nx z5m w*urred 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 ma6 j77i55ekx7 /d zyycmtk.klvss of 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, e5jkkct zyv/x6 .d ye577 li7kmstimate 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 thu ch+v:p .toi0wqx3a 4rown straight up by someone who does 80.0 J of work onqap:h tcwv 3+o 0i4.xu it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically withb2q1 )shxvi/b;vywk pph7 +5 (jweg9h an acceleration by a single cable. Determ1/b kh+wq;y (5hg92ip e )hjsx7b vwpvine
(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 q1 fjfzw3z7)gzsq 3*ay4 gk4rmuch must this sprinzy3)g4zkf aj 3z q4gfwrsq17 *g be stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from onec;zn /u1zq j;e branch to another 1.2 m higher. What is the change in potential en /j;cz1;unezq ergy?    J

  By how much does the gravitational potential energy of a 64-kg pole 1b8j2 z) g4o4upvxapvvaulter chanxpb p1a44gu8vz) o2jvge if his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal sboj;( d ss9u(+/3 mr,k dybcplfbs t6*urface has speed v = 65 km/h when it strikes a horizontal coiled sy*us((fd9b bo;3 pjlrmtks6+ dc/b, spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 ;nc*vvyw82 *w 5.qqxh3zetcmn6ns / s m above the ground. What is the potentia q8nysmz563;w *vsvcxw n*n.teqc/h 2l 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 ofn13 9qmj1:zaz0c lrfx a 3300-mc1:n 10lzmxajf3r9 zq 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 9 f.j p;z bse3.nbcgy50zvz0g pfk9/sq e2pa6next 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 enjzfs vaz3zb 0069pgkc. ysp9npeqfe;5/b2 .gd of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vink ( yf4r36m/-airbnqve hanging vertically from amv bkif6-/aq3r y4(nr 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 fz- q (+9t-l7ycefso ewrom rest, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a goa.bun*e+ u +fmh-)ushove 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 e6x/ ,hns3f;jqo.7gtgj astjk) 6qz -y nergy is transformed into gravitational potential ene .6;tk/oazfynxh,jtqg-jq 6 sgj) 3s 7rgy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps ve 0:n /edz* d(fp8deakvrtically upward from the top of a platform with aek:*8nddz /e(dfv0pa speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose sp;oba9u v5-z d hec+u0wring 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 ba o0e;9+-ahvcd5 uzbw ull 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 looped trac2/. mgkclp6/aiz ap1vgya-1h k shown in Fig. 6–39. If -/1ya2 igga1/pp m.zhac lk 6vthe block is 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 stiffness co i iz484ex3hpod(i(-i + vi(pdszj-cqnstant j(+(pqiidoi8 e czpz44ix v-3 h-(d sik), Fig. 6–40. The block 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 q0hcpg3 sf71u bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculatep0u3h7gc qs1 f 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 Fiqh 4fmx3r0eur/2am g, g. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calculate thh/rg2,3emm ua x0r4qfe speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed n m(f/c,s* mwlo 26dloof 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at thlwbq,2kf8a m+ e bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top, afb8l2wm q+k 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 passengers.

  A cyclist intends to cycle up,ua7 zsh4hwyv1 ew15-kt b h1c 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 travoo6 r 9)36iviuxdxg8xeling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this x 9)3o66vrig ioxdu8x collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 mx9+,r2x c1ci .p (gnfztyjokfl.k ) q:0nnz 2j high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was gcnjf)2io2jnc kg:(f zp +9qx,1n0 r.kxlt. yz enerated in this process?    J

  A ski starts from rest and slides down lw3fb kanp4m*c *:1q07kmh mva 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 iy z7,krgpxkar b-98g wt n)z+6(nhd.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 bounce:jn1ch8 zkax.s back to a height of 1.5 mh81 jc:xa.z kn.
(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 acrg/nh);uj zo-:a r 2vnooss a floor with a constant horizontal fogh/z2:-o)n uovr; jna rce of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a spo+j)eep (tj l ;l** y5vsolvm+eed of If the average force of friction is equal to one-l* o)*v(pjmvy ;tel 5o+ejl+sfifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady 5jt );y qai*cqp,b(hb 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 ze;: bh5 dqz8ffirmly attached to 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 cm beyond the equilibrium position before stopping and turning back. Whz8: qh;dfb5 ezat is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spring, Firq 1.;+cy zav qzribp6g(.4 fpg. 6–40. The block can slide along a table where the coefficient of f(.z+g .1fqir6v;za4py r qpcb riction 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 shuttle used z 0vlfq+l*c)na “glider” (mass of 980 kg including pizcl *n 0l+fv)qlot) 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 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 lfrnb+ flpm 7* -k-(:cyfb1mma 1750-W motor to lift a 315-kg piano to a sixth-story window 16.blmm*ff-mk c7p 1n(-brl +yf:0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the p6x2u yd mm7t4average forcu6dmx2 pmy4t7 e exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.42d t*+w)ora dw*b / j;ywtv7n58x jclh s. What is the average power delivered by the engin*w b5xajh2d+) jrw/yl d8;* cowtnv 7te?$\approx$    hp

  (a) Show that one British horsepowebmx)y2mtj:, ao/dgm*r$ \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 “kilowatt-hours.” gk kqj3im-v4gmpep d *u/.p 7ql07u y9
(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 1150-5zjj,8- ynax wix7(z mkg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the ca,mnz jy8x5zj wxi7 -(ar traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp moto; 8f+nojqmy-ir do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-ka x8rip0uc7 5e4/zm xs)hqd 643k rzgrg shot from rest to 14m/s If this motion takes 1.5 s, what averagup/qr5046 reri)3gxzhcm 7 xkdz4 8sae power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute throu*e4mc 0kvqguqo q+ ;c)29e*er 3t fptagh a height of 3.60 m. What output rating (watts) should the ptp0)2uk*e4t9e +;qqmg*acoev r3 fqc ump motor have?    W

  During a workout, the footbac j3u6e.. rt9p s9ujzs2e 3lkza/7wgell players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an angle of..7g9z 36elpercuktusazjw/29 3e j s 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 xokd/(no *z0 xl9s g*ia 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 outs20aih)6x-8xj nuccr 2mqk2 cput of 120 hp. How steep a hill can it climb at a cm s cc 0ucnax)j62hr8k2x qi2-onstant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepowewju5 q93uh/; ss,td jzr must a motor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient ofw u3 9qjd/,t j;uhss5z friction is 0.45?    hp

  A bicyclist coasts down a 7 i/l9vpc.sbo z6s z3xm)u(v2z .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) bumpers” that/k wimm; sw8zco*6s4q 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 1.5szw i86 o*w;m 4sc/mqk 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 fow,k bbyz3 (rx3i7b +5ge 5ccpirst shelf is 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 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 53zocyrkg ew(5,p 3ibc+7bxbfloor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the c em;ysl 93bw,1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed 3wcmbe 9 ,;lsydid 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 sli1vw 3,gu e-gm9k+f5bz- ekxnf ding without friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very gkekgnw5z +e-fbxu9f ,mv-31 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 i0q+ o5 txjx :j+;evii370 m after jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived wit 5ie++qjx;vii0 x:ojt h only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose othew 32kpe oq:9t-c7q qvcr end is fixed (Fig. 6–43co3pq7:9 2vet cq-wkq).
(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 es9zk2m2ho*8 x;fzv jtop of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Ca;zm vezo2 kx9h*8jfs2lculate
(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 elevatoyjdp91r0g/cdlk* w9w r 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 (q;8v(kd -mh: ze ey;tfk / :nxqwas0klifts can move 47,000 people per hour. If the average lift carries people about 200/ 0n ahw:kx(dm k;y;:qse-zv8eqkt( f m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m before9/ qz9alck- bc/l)-)0ib yxmbkq/ztdr5vp k, striking the turbine bladesy 0lx btk b/ /r)bl d-cq/)zzm-9aq,pic59kvk. 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 loop (Fig. 6–44), the falkyp dy4 turs5oa 06n /( 8*r5yn/hbdifference 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 yryp/ybnt5f/al ka0 *s6u 4r(5nhydo 8ou go through it.    mg

  (a) If the human body could convert a candy bar directly iniinx pj+jri 0ia3h k/ltb01. 4to work, how high could an 82-kg man climb a t/30iihpn ix 4b0+iraj.j1k l 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 upwa8 ( zy25sb:8l4dydh fs la/bhard 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 0tqz4 gr8e xx:/mly6))zqs vq, 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, wez 0t8 lsr)xvq: x4qmg )z/qy6hat does the scale read at its peak?    N

  A 65-kg student runs ayy s1,m5awa,; o8df qgt 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is ze ay;,sf,qa g 5ywmd18oro.
(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 7qfjr8rbndo. e,.i.re; hg y1; 2-kg athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accomplish 8jrneeqhb r yrdg; .;o1,.i .fthis feat?    W

  Some electric-power companies use water to store energy. Water is+ctbwrq+ldn(8g37sl 7 c -m zc pumped by reversible turbine pumps from a low to a hi tngqldb7+w8c(c7 +m-rs cz3 lgh reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cth-5 s(qwj56y ko,zbxut in half. What is the spring stiffness constant qkw5,5(hosy tb-zx j6 for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough . mpohmwyn1)* f66z)dl t1e3fxm ca3w 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 34l5y. :9 jjxge gdh3d*s;bru n.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional 5 *e l;:ys drg3nbxujghdj9 4.losses.    s

  In a common test for cardiac function (the “stress test”), the patien4wm nb: , -i*5jvu7vsn il,k2j7rotlwt walks on an inclined treadmill (Fig. 6–4jil vn*m:, kl 75-ov ,uw2tn4isrbjw76). 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 upward a distance of 500 m, irut+-r:b 6)9wufwgrc uf,0vwhat was its velocity whe:c-ufg fw)9, rv+60 ruruiwt bn it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheelp6 p;qh r)f6c)*jgez1zin ko* from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up t)ch*;z6ef)zi* k 1 pqgj6o prno provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s