In what ways is the word “wonv 8-yzybqvt9: 3.ijbrk” as used in everyday language the same as that defined in physics? In yiz.9n-38bbvqt j:vy what ways is it different? Give examples of both.

Can a centripetal force ever do work on an obxctqejg8 av6u0v qr79j z276lh*lp s+ject? Explain.

Can the normal force on an object et 4qa4j5)pb9 q)tdv*jm-uywmp y (g3aver do work? Explain.

A woman swimming upstream is not moving w99b7ktbso-fw8l 8m jq ith respect to the shore. Is she doing any work? If she stops swimming and merely floats, i -w omt98b8jqb9s flk7s work done on her?

Is the work done by kinetic friction forces always dh-m4b*qslirydo x b4 :e*s9; negative? [Hint: Consider what happens to the dis*m4qir;seh y bl49od*-b xd: shes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are doing cns0vu xa*o/zd1 hfk6n.vw- 8no wd6k z. n1ou -0a/ hv*nxw8vcfsork?

You have two springs that are identical except that spring l ia4a e uwmh pto3gkneqen 8wi:5r-/*9 6s stiffer than spring 2*p w3/r nteenw q om9k8g6a:e45hiua- $(k_1>k_2).$ 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 s( fw/ emj4j.ton a block that is free to slide on a frictionless surface (Fig.6-30). Tht.e swj/ fm4j(e block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitation,c bi/lzn gf.t8i4cf gha;0x l,qgy+ c0vq2p- al potential energy change when you jn zc2xcyiglgh 8i 0pf cvq -g, b0.qftl4;/,a+ump as high as you can?

In Fig. 6–31, water balloons are tossed -+)c0+n q vb:laoflgerwwgk qe;3* +pfrom the roof of a building, all with the same speeab*+g; +prk+ew qg)qn o vec0-lf3w:ld but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a pofv)mxme eo6j e28qb7,pum q u9 .izm83int that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On 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 swiu3 mo .bev9q2 xefmpeu m6)m 878,jzqing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a tabl c ;igm*ksi7ij0y, cx-e. If you compress the spring by pressing down with your hand and then rei j,7*mycx-k; gc0isilease it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a stee x fkai-b8*ri)l wire (Fig. 6–33). The instructo)k b rf-*iax8ir 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. Why?

What happens to the gravita m7z:+(nl.r nef3abditional potential energy when water at the top of a waterfall falls to the pool bela e+nmz dn3b7. :lfri(ow?

Describe the energy transformations when a child hopsm edcc q6)ruv44n(2-qsobn *ew pg 6+a around on a pogo stick.

Describe the energy transformations that take place when a z-af12 .f0i xkfet f0cskier starts skiing down a hill, but after a time is brought to rest by str xfie0 cz t21.ff0kfa-iking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of 17ba6 5brukap0 cd(xja hill of height h and slides down. Does the velocity at the bottom depend on the angle of0u(xadbkb6r51 a7 jp c the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step onbh; 5 tzkatyf31 a.4ht ,w74ks ktd9over a fallen log in their path rather than stepping on top and jumping down on the other sayfk, b7tza w4t5hn9 s4otkh1;d t.k3ide. Explain.

Two identical arrows, one with twice the speed of the other, are 1nv(a +p z:ykyfired into a bale of hay. Assuming the hay exerts a constant frictiona: ypzk(+ 1vynal force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in termgb w--:wl/:bhy ehsbm )-m 1mls of energy, (a) ignoring friction, and (b) taking frimhbs 1glb/my -::whml-be w-)ction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can .uwc:6lcz8 hn it rebound to a height greater than its original height?:h cw86lznc u. Explain.

Suppose you lift a suit ,cl1 a,vy1qvwcase from the floor to a table. The work you do on the suitcase ywv, v c,11laqdepends 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 of the suitcase?

Repeat Question 22 for the power needed j7n+ -84ef dlsxj-cbapq4s1 wt pwd-+rather than the work.

Why is it easier to climb a mountain via a zigzag trail than cw*fg, *n y bjb+w74tato climb straight up? f,byjtbcw *+7wg4n*a

Recall from Chapter 4, Example 4–14, that you can use a pullkrru7rc jft)/52k8rq ey and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must 2rq8jr7r kkr )fcut /5be pulled up? Account for this, using energy concepts.

  How much work is done by schvv/ i) k1djezse3.wwb;3. the gravitational force when a 265-kg pile driver falls 2.k)c; zwsh3.s/d.jw vv1b 3e ei80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. ztt0fnhk0o68yy m 1h3nh:z c:u 1q4 anHow much work is requi3 6nuzmhkt:0t y:of10 qc84znanhhy1red?    J

  A 1300-N crate rests on the floor. How much work is required to movt7ikll p ow3:)z 7q4rne it at constant speed (a) 4.0 m along the floor against a fricn4k3:qlil7z o)p7w trtion force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the mov,a; /g-bvzxtu) km s,ners do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor ),xmkusgz,v t a/b;n -without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is acceleratamm9.f sf9 1hkwqy5 )ted by a force across a floor at a rate of for 7.0 s. Find the net work do 1h9 )fkm9ts .f5ywaqmne on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table.c4cpxq v*hx t5lz6s58 How much work hz58l *xtvx4cp q6s5c is required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35l/kn2rq (gky05 ql2zg can be used to liff objects we might not otherwise beq lzrynql2g(k 2k g/05 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 2 q5v7*ibazjb-5 0gdkq8° incline and is kept from accelerating by a man who is pushing q kb0jgdbz5va7i-q 5*back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give al1j;3ptd3 n oz0qt6 nyswdl;: helicopter of mass M an acceleration of 0.10 g upwjtdypnlnl z0d1;:w 3so; 63q tard.    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 w;9i uj4it96ul:zpddis 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, var)kl; ;bjua. tens+ (qmies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x = 10tb+j)qau;.;e l s nk(m 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 particl*:ot)m h.lhp)tnny+ghv0) v u /b/bh de 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, an oxygen molecule, witb 8ze7cnkl6k*h 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 factoqt.u6l k 5f9*o lbrwn)r 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 stg akb :6h ld,z12mteo9op 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 105 eq.+5h691njorn egc kkm/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average foel vvx,x(f2y +6d (8nzx.iedtrce of 110 N onf ln2.zi (y8,(exted dv6vxx+ the arrow over a distance 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 f-iff) 7i mn0xdielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on the glfxif)n7 -im0 dove?    N

If the speed of a car is increased by 50%, by what fact2bhh 1;nd7 jb y2ozvnfu9 n1p:or will its minimum braking 2y1j 2bu9bhn1n;pdn hzov:f7 distance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigatorspjmt1ou3- -vy1y 91m3 kijjc y 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 estit93m- u 1cyjom1kvyjy1j3-pimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at et-i8mc1x a4v1 rw cry cnr2l*/cy:b6zf54vh By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a p1 -45ve4txm2rzy cb r chyciw1*cnla : rf/86vitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who doesl fz9 nhvj )z8 j;kwny.(o kv:a;98gcn 80.0 J of work on it? Neglect air resnf( 8y;gnlvw h.vjza)9jk;:9ck on 8zistance.    m

  A 285-kg load is lifted 22.0 m vertically with an accelerlhtdh9od+.mw2 z t .w4ation by a single cabledo wzh+h.td .2w4t9ml. Determine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much musti9dssw9/y2 en m(p9hl this spring be stretched to store 25 J of potential9 wysp9hnms/9(e2 ldi energy?    m

  A 7.0-kg monkey swings from one b u:kem6y pm-1y1h z6dqp ,pson69okw9ranch to another 1.2 m higher. What is the change in potential e 9d-6mp 1opz:so6nepyh1 9qky6um ,kwnergy?    J

  By how much does the gravitatio 6lv+-s izn/x w-r;zcpum7) r3-swpvdnal potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during thpcms+r- pzr7;/xvw il) vw nz-s6u3-de jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65- xs/d.ihfpr*h 71 lqw km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness con*i .7dlhs1fpx hq/ rw-stant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book ftmk (8 , jdnbulqkkp0i v ;6284qvne(lrom the ground so it is 2.20 m above the ground. What is the poe( 8vl,lp u;dk 4b06njnk8qitv m2k( qtential 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 3300-.8mgpl,n .3xy 3nhhaym pea ap8m nylx.nyh3hg.,3k.
(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 ney 1m j5axnlx bs( :x.a2- bevt*2oz2cext to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a o.xxxbasm-n :cv(15 be e t2jl2z2 ay*2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a d( rdflhhvj.z4 pt)58vine hanging vertically from a tall treetd jh(5z)vp4 d 8lhfr. 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, startingtwfeyjwm;t.s (l -jgc0grfwd64 p)h h-r (-4h from 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 giveq4t;3/xoh(o va d l-ron a shove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed vv/ d rkv620tminto gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the b06v2vmd r/kt var with a speed of 0.7m/s.    m/s

  A 65-kg trampoline arti*stbt,j /0;1 mev: i2 uxnlhv uz.yc8hst jumps vertically upward from the top of a platform with ti/x vnleczbu8hvty*0 2m 1.h u;:,sja 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 sprin v+,6 zx44bpup1gmo xayg)rj) g stiffness constant is 950N/m is attached bay + 1xmop x44v6)pgzugj),rto a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides withsyrxewt y8/ijeb+m) jo.() kn 8h6)mjout friction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at msb y rjjy+t()/68.k8wxo)ehei) jmn 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-a)fx b+o ki+1lm dpwj,0c 6qu of a spring (spring stiffness constant k), Fig. 6–40. The block is givew)c ,uq0xok 1ida +fbj6+ -lmpn 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 b; u3+tub3ff z+r dqz-9l9hggxridge. She is tied to a bungee cord whose unstretched length is 12 m, and 33l9x;zufr -z +qhdgbtfu+g9 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+ 6omu jor9gz(–41 is dragged up to point 1 where it is released from rest. Assumijo6+z9( m ogrung 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 spu g.dd6sq6e/gl zz3 z9eed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of an elewu v. +yh*l3vsvator 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 cvs3vw.uyl+*h onstant 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 a e z6ij4rqab ab/g(k;9yo5, l0monk)k 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 tr 7,sqhi brje/ffl3,t 4f( a1avaveling 95km/h in opposite directions, collide hea h3ajsf(bef4 iq r,/val,tf1 7d-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and rea15+f jrhshivheo 95/f pnlri12kb7*pches the bottom with a speed of 2.2m/s How much thermal energy due tkeho vji+ihs rh1 9rnp5lb*f 15p/72 fo friction was generated in this process?    J

  A ski starts from rest and slides down alb3u 5ai.2rhgs) w0lr m dv 8+zdvcx22 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 f+jei 5)ay q-vgp5stw ay66dj7rom a 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 ofp 9 3ta ua1yikp+)t5td 2.0 m, and it bounces back to a height of 1.5 m. 1aa )t t5 yd9uiptk+p3
(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 frodrp3igy(0 k0vgk4 -sv+g,nivm rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionls4 igv0gr-gknd v,y 0v3 (kpi+ess, 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 ind29ol*m)m1dowzp1*9id f cm a Fig. 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth ofdp m*d9)mf w19m2d a1ozl i*oc 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 fo 26 nhk0-sr /)qcnyzzqot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal jevccay0nbh2 ic2 y fw5m3:, 3spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when abc3:e n05wy y3v,cm 22hcfijcompressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spring,kuzdk5uh9 e gbuggengmp1m:w-9.4 68 Fig. 6–40. The block can slmgu8bepeu nhguw 5 g-9: 1.zkk9g64mdide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg includis) wf(z :mza.png 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 land .pwm:z azfs()ing 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 a 1 b dh0/sq(( uu a5nzy80fky, 4ybsrfx(750-W motor to lift a 315-kg piano to a sixth-story window 16.0 m above0adkqxsfbn z u y/((r(0yhb5 ,f 4s8uy?    s

  If a car generates 18 hp when traveling at a steady 88km/h what9) wi)gl-0e)e;uf f6e n elgqw must be the average force exerted on the car d6 flq n wwg-ef9i;e0gu l)))eeue to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/pws 0w,ifdj4jl/vl/ suayh*1g z/ c/7h in 7.4 s. What is the average power delivered by the sd gs/iuh wpz la/7j,0lfy/ vj/c*14wengine?$\approx$    hp

  (a) Show that one Britiyi(z krzwu4) 2sh 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 the form of “kilowatt-houl zqxaqug1*0g8lq02 k70d bbi rs.”
(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 downvzcbp1 cb09i7 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 7 c9 ibv0bcz1pkeep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hn/ k jaw5x+s)prhpo86 7xw)1mw 1zoaxp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kgkq/7+1 hwme pfo3ti ,y shot from rest to 14m/s If this motion takes 1.ot /pk1f3h+i wyqem7,5 s, what average power was developed?$\approx$    W

  A pump is to lift 18.0c i hz yih(804xvask6; kg of water per minute through a height of 3.60 m. What output rating (watts) shs4v08ah yi(k;z 6 cxihould the pump motor have?    W

  During a workout, the football players atfb i5mx m8 ekh8vz-i(-5hf5reqnj5b1 State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an angle of 155(ex 8h 8mfq-mkfzehviib 55jrb- n 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 climf57idv.+q u4wv)fta r / c6ooyb 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 hill can b984h h cfaru.it climb at a constant speed of 75km/h if the frictional force. a8rf buhh49cs add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be4tp b2oh *c8kb ecv/1q able to drag a 310-kg box along a level flooq 2ve1*/thockpbbc 8 4r at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts d*cdzd /dnt2*z r tdz:n e5a+1rown 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) bumpers” xl+7gci+jy wd7 2;oha 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 spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by r 7 ;oagy +2jwc7+dhlixamming 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, anj: b mzb: )(*q,irswded the remaining four shelves are each spaced 30.0 cm above thesmd)wzb : :b,irj(*e q 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. 6–42fx 74hik 5d:bv) in the 1936 Olympics shows that his center of mass ro 7ivh5bx 4:kdfse 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shzcyaxik ;r64:unih38own in Fig. 6–39 is to remain on the track at all times, even at the vx84n6;iu3 ihaykc:rz ery top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without his para0br/i,mep4 oo/ y1yd kchute opening. He landed in a snowbank, creating a cratero kmbr0y,eypo /id 1/4 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 e3be-eq:ym5xs a 84yoe l jr7(length L whose other end is fixed (Fig. yee 75a e3x4ljyob m (q:-8sre6–43).
(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 tor.ubfbvo 7p64j15m zp(v;wfo1sgun7 the top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Calculate wmrobgus7nbz6 1po1 ;ff4v75( .uv jp
(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 bred6lb)hvjfg-3d asta ;67 id. jaks 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 Cal bc.6sef/ hd4hifornia claims that its lifts can move 47,000 people per hour. If tdf4b /c s6h.hehe average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rabkf1wtm2(matx ;hi -: te of 650kg/s and falls vertically 81 m before striking the turbine blad (ht-k tbwafmxm;1i:2 es. 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 rolled:d. 2 ;r2jzeq0c furkx5i gg4r coaster with a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is a dz.jgrqfx4; ki225:gdrc0 e ubove the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a cand(vu so0vai*gk7 by1hj2o :0cqg18 m pay bar directly into work, how high could an 82-kg man climb a lad(v8p2i 1y gua07 v hos g1kbc:o0j*maqder 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 upward 3sods(fd9hriq;x acg0j4ts dq 4h9j 94c; 8zjangle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale compresses 0.6ir b(yqvwxmx2tg )-cok .s )iw58z;- s0 mm, and it tells you your weight is 710 N. Now if you jump on the scale from icr82 ;ssw5y(x)xoqvig.)wb k tmz- -a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs apjmne2p/,( zw* xce g)t 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is zepe/(j )ncpxe,*z2mw gro.
(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 wo6 /jxpemu sxn8.e52athlete climbs a vertical distance of 5.0 m in 9.0 s. What minx6e./m2 8eonj w5usxpimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped by rez3lia (8pidv4versible turbine pumps from a low to a high reservoir. To store the energy producedida zivl8(p3 4 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 d d1k9t3,ar8lt ngb3;. dokoguu-6dvk is cut in half. What is the spring stiffness constant for each of the two resulting spri l-3td 9bd3g61oo a8ud.udr kkg, v;tnngs?   k

  A 6.0-kg block is pushed 8.0 0sas cuis96o81 q( 7x ccue 5fhqm+f5dm up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate frommmu-lwx/7x ,z 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same,wx- u,7/mzmxl and neglect frictional losses.    s

  In a common test for cardiac functio6l )dtdbx1b qohi7-5hn (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 1-5hbld6 tx1 h d)ob7qi5 $^{\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 5pt8 +rv pga:ev-ae/ xyuq20/p8uce,m00 m, what u/ gp t8pyqecx,a0v :emp-2/+eur 8av was its velocity when 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 w)ygmksc p8 8l7heel from 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 8smc78 y)kl gpis its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s