In what ways is the word “work” as used in everyday language the same as tha4 ai/cyt q0-mqt defined in physics? In whatt-iq a 0qym/4c ways is it different? Give examples of both.

Can a centripetal force ever do work on an object? Explautp4yqzoqp8 6+ w4y :kin.

Can the normal force on an object ever, hi hm,k hf7oe79tjklzd5k37 do work? Explain.

A woman swimming upstream is not moving w (z7ljeaahfx:(j7* epith respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done on 7jxez:*(fa a 7eh (ljpher?

Is the work done by kinetic friction forces anchmo ;yf x w;m6r.2d(lways negative? [Hint: Consider what happens to the dishes when you pull a tablecloth fwmo6y. mrx2(;hcn;d out from under them.]

Why is it tiring to push hard against a solid wall even though you aretnjjd(2 vkii4 dq2fjk6 a, cfc; qzh*2;kdr5- doing no kfhi ad jd6 ;;qd-4jkc225qj zvn( tick2*rf ,work?

You have two springs that are identicap*l:d2v39y-m u4ejbx./ntp ,r d xmicl except that spring l is stiffer than spring r.:udcixxjp43yv 9bpmtm l*2d-n/e,2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block t n7 fpr-z)p*dbhat is free to slide on a frictionless surface (Fig.6-3)n zpf7db- *pr0). The block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational po: inpub+vx: p 8ajlw5;tential energy change when you jump as higvpx5:jn:wi+l; p8 a ubh as you can?

In Fig. 6–31, water balloons are topdz1- dsygz4/ ssed from the roof of a building, all with the same speed zg4 zyp1d-d /sbut with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a heightmblzi(5)xw8 rxh /wym-1a n+g 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 directe/(gl -n8h1zr wm+yxxia )mwb5d upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress the spring by ,); - hvrrwyly5oae;mpressing down with your hand and then release it, can the spring leave the table? Explain, using the law ofl)ywmyrev r5h;-;,ao conservation of energy.

A bowling ball is hung from the ceiling by a steel wire 3qb7p1chytkl m940gh(Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it.yp0 9gcltq3 b1kh47 hm Why?

What happens to the gravitational potential energy when water gba11f h2ksv/c9 i3zvat the top of a waterfallkbvcs h 3fv 9azi1g12/ falls to the pool below?

Describe the energy transformations when a child hops around on a pogdflwk2(y;ha/:wk z2 y o stick.

Describe the energy transformations that take place when a skier starts skiing dbc;b7e 18u szeb7 wd3loz:uf (own a hill, but after a time is brought ceedow(8zb7 u:b z1;3fsu7 blto rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the tb4 h*x 28axzzqop of a hill of height h and slides down. Does the velocity at the *hbax2 4qz xz8bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer m3lgd;h*8 srnto step over a fallen log in their path rather than stepping on top and jumping down on the other side. Explain.gshn;d * l83mr

Two identical arrows, one with twic1 5aidv8 ujr6ve the speed of the other, are fired into a bale of hay. Assuming the hay exerts a co1d5ji 86v vuarnstant 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 pendulum in terms o0kz4 k bx:,elnf energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfatherz0x b n:e4,lkk clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than ev rdutrt0i*.y.h)- sits original height? Exu rdt.iyve0s-h)r.t * plain.

Suppose you lift a suitcase from the floor to a table. The work you do on vz rj1l k1.2ie 0:fttathe suitcase depends on which r t:zf201kl v 1.eajitof 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 rather than the;koze sv-8 - e8 x.*qh udm2gjaxj98wl work.

Why is it easier to climb arxm a2f19b/ yx mountain via a zigzag trail than to climb straight uxax b2m 9yrf1/p?

Recall from Chapter 4, Example 4–14, that you can use a pulty q )(+pidegsz2a+vu: 21 tedley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is rais1 evpgye +(zuti 2adsq2:dt+)ed, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the c63s(p w ld.lggravitational force when a 265-kg pile driver falls 2.80 w6s .ldglp3(c m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How muchx.q7a:6tm/ idqs(k jg work is requia(xs6t.i7jqm g q :kd/red?    J

  A 1300-N crate rests on the floor. How much work is required to move it at conq.vi;n/( u7k0bk t yrnim* 6w) 8mnqhystant speed (a) 4.0 m along nv; ) uk 6*.nbm/8nykiri(q7wq0ymh t the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (hor4qcbv t :* no,avrol5zr )rb5)izontally) pushing a 160-kg crate 10.3 m across vbvoct * :lr, )) za45nrr5obqa rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a f fn8 nlr9v3qi8mlt y-9orce across a floor at a rate of for 7.0 s. Find the n39 8q nint8ly-fmv lr9et work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a kh)p y wzh f.e61tbr9+table. How much work is required to stack them one on top of an rbyzfke16) hhw+t. 9pother?    J

A lever such as that shown in Fig. 6-35 can b jcfo0g7zdeb2 w2s g41,ltj l+e used to liff objects we might not otherwise be e1gc t jl4sdz,b +2of2g07wjlable to liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° inclinerv3)c ,d)s) o+pk rl3a2p sy 8rcdzab6 and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coef sy+az3, r8 kald2)dcrb6)co)p vpr3sficient 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 ggi*i4:1 nc2,kmopdda helicopter of mass M an acceleration of 0.10 g m2 4 no1gcig:i*p kd,dupward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance axis is linear and that a8 mo6u3 fj,alv d5q/tr nb:-n$d_{\mathrm{A}}=10.0$ 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 shohq2x5 hovh 5e8wn in Fig. 6–37. Determine the work done by this force to move theo8vqeh5h h52 x 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 exertesh4 slap 3*5ied on a particle 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, with mass oe 6cn +hj.+xbqf $5.31\times10^{-26}$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 arrow2choo e5vy js,d)3hp*k6 th l6vk7)t x is doubled, by what factor 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 ael7 vs1kx:esi 8j d.1dn 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-kgcar07 . hxeakz1ro traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an avera xaky29.uaj,mge force of 110 N on the arrow over a dista9kaa2mjx, u.ynce 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 y9(oyp e7rcj:ielder’s glove backward 25 cm when the ball is caugc 9:oey(rypj7 ht. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its mth.a3gc ad 9u/ycz3kzm*d:o 9inimum braking distance be increased, assuming3y99hc:ucoz azd.kt/* g ma d3 all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigatorsb0o 3: tgur e2d.xw7yt measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use thb0o wd2t:t. 7g3ureyxese data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the tz0(i) jcwa im+hcd; o,sic+.hime it reaches the platez,wmich ()o ;a+dic hsjc.+i0 , it may have slowed by 10%. Neglecting 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 by someone : *xzo w7eyxeu4--idm who does 80.0 J of work on it? Neglezi 4exoeydu7-*:wm-xct air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceli*d1jgg e .g*n )5agihh+otb(;ll0gk eration by a single cable. De1g(h)n tld g0*kbl*e o5i.;i jgg+hgatermine
(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 7xsa3e lzsz, ,stiffness constant, k, of 440N/m How much must this spring s7zle,ax, sz3 be stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher.qb9u 2w6 0jrhz50v ufm What is the change in p jmqf2wr5buv6 9h0 0zuotential energy?    J

  By how much does the gravitational potential energy of a:eqdjs5y2ln s,ih xw pv/h+:8 64-kg pole vaulter change if his center of mass rises about 4.0 m during thevh/q82i5 :d s+,:jyweplhsxn jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h whic;rj2++uw q.:k: khl*r u*bgz h*7r nclj0vken it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constantnr**zhb:c :;wj+0qj+g uk.hlk2cv k* lriu 7r of the spring?    N/m

  A 1.60-m tall person lifts a 2agqf+lzeb j: ay33s7 8,ck qt+.10-kg book from the ground so it is 2.20 m above the ground. What is the 3tk,q f :e+gcsyajb7+a3lz 8qpotential 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 33008r*sy1b ki b5qm17sx- o)1y ruuiont 0-m peak. ix1*n q y)ok178b1m5t- su0oriry us b
(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 flgh-e,qx-(pp6sep a gmdx. *i0-y 2bhangs vertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line upy6- slq-ge,* (-pe0.fidahp2px gb mx with the ruler marks?    cm

  Jane, looking for Tarzan, xs2pav ljhok) v5,1a 8is running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing xa ov8ap 2j1lk,)5hvsupward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a crx/c dhb o2- .e9p0tg8xx 0yhfrictionless 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 givew0 ryun+btznalhl q j79,; 5v)n 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, Fraxx2n )4hh(xw kn’s kinetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the gro(x)k4hnxwx 2hund in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a /y w1yn5qw4*2 f /cdx/ kdmam9aj 4tskplatform with a speed of 5.5mtfsc94/a/k4n /j kqm1 d2y x* dawyw0 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 spring stiffness constant is 950N/brhj1 d -5c55ibc. rle n4j 9jgk2ps3em is 3jkr9jj5 ncr egis e5 lh-2bdb5c41p .attached to 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 without friction along the looped trackxr- .,-2x uyfqlh xx;z shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose -xx2,;r.lhfx-yu q zxradius 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 st.l(ukl/ v: w*qsyf9lriffness constant k), Fig. 6–40. The block is giuv frl.sl9wk lq/ (*:yven 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 z cop(gxy **5ian k6/bunstretched length ka5o* (nx*cib/z yg6 pis 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 whe;2we by k (my-4azwca9re it is released from rest. Assuming no friction, calculate the speed at point(m9-wy 2zb;aakey4w cs
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angle of 3+ 9(n;uls2+(alc dj 8xmmmxtq3 $^{\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 auck -f3xr (*1;mk v6.kr+ iaw spo4spa spring to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness co;a .kso6+w4 iksv1*crpfarkxmp ( -3 unstant 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 uob13lg; skw7 n2t(xqyp yb1z1p a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in opposgy,yu0r6 zya2ks x :x/iv)vm+ite directions, collide hea)gvrxs2yy,i0x6ka / zvu :y+md-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 rea6(wp 9lywoeb,oco (0pches the bottom with a speed of 2.2m/s How much thermal eneb(o9 lpeo(6y ,cwpow 0rgy due to friction was generated in this process?    J

  A ski starts from rest and slides down a 22 hf*z da *3gffzna.wsn:j355k $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above the g 8 y*ccz-+lyylround.
(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, q;vx4 ka8a8,q uad*rp and it bounces back to a height of 1.5 mkdq 88*u r;pxaq,va 4a.
(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,:u6 zvdrn m,7b is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. Wzbn:r7 ,v mu6dhat is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 pass9,g/nfpz 1l3,b z xgates point 1 with a speed of If the average force of fr3/zzp9gl x1a, gbf tn,iction is equal to one-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 tw)4at, qx fi*xhe foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontqd5(.4*i no2z2 hnfrftx5 b yval spring (k=180N/m) as shown in Fig. 6–40. It is noted tha2n5x4v i o2fyzb(*f. q5 ndhtrt 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. 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 b.qmk1a46tpx spring, Fig. 6–40. The block can slide along a table where the coefficie16 txqp akmb4.nt 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 p3epi 8a 3vqx:h rx5uptl2)-uused a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider evepi 38xt:3)a v qpl5x re-2puhuntually 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 a 1750-W motor to lift a 315-kg piano to a sixth-story wim 3vx 49xjov sjw3g2)zndow gv3 34sjwj9o )v2zxxm16.0 m above?    s

  If a car generates 18 hp when traveling at a st5v 4zykb(c:ds eady 88km/h what must be the average force exerted on the ca4:ydzkb5 v(sc r due to friction and air resistance?    N

  A 1400-kg sports car accelerates i-tdvbmv),q/k26, e n aoauu- from rest to 95km/h in 7.4 s. What is the average power 2viat)v -mu/k-aqb, u ,dn6eodelivered by the engine?$\approx$    hp

  (a) Show that one British horsepygf:)lt n;elh/pup: +7aa u-dower$ \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 amb a*6cz*z4 /mm whvd6ns 3v6ire often expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows downe8qfnyya/t 7d z 3q0iv)r8g5o from to 65km/h in about 6.0 s on the leve)ya3zi 7 yogtev nq88/r5fd0q l when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0fr9vka0(4 ) zhioxon(-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot fro w5gwusx+9;svndh8/nnh .md(3f1p,nja bs* wm rest to 14m/s If this motion takes 1.5 s, what average powes;xfw.h 9 mdw(u/*+nbwdj38,nvgan5spsn h1 r was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a hdd0ccl.ck um+d t)+, xeight of 3.60 m. What output rating (watts) should +ccu0 +kdm d)tx,.lc dthe pump motor have?    W

  During a workout, the football players at State U.8zy, h gx-vls, ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at ansz lg,yx,-8h v 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.kvb+m0j8jci 5t* en:u 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 it c6es 3n. lx4pqqlimb p4 l6q3.eqnx sat a constant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to dr4dea ez.s f.l u:p,ihhq3(wf 4ag a 310-kg box along a level floor at a speed of 1.2m/saph,( .fe:.l 44weishz3 uqfd if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dohe cn 7-2zk.dn2b5dfiwn 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 bu9x)mhsoy4w 4:*yd9jioqw f qjq.b /a3ilt “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers)*4ow y qq3qyd9h/ bfsjim:jao 49.wx permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf isj pcdw-n:n06c a/ p7ku 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cn/kau6w dcp- n7:jp0cm 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 Olyml, 3(l8qlknpqf*f9n, eve1 r rpics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if hel 1flfe8rq3*qn9k er,nl ,pv( was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the loopepb r65jn )pv9yd track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loopy 6v95jp) prbn 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 felu 1s nndh60e7ll 370 m after jumping from an aircraft without his parachute opening. He landed1eu sh7d n6n0l in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s 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 ho,9. c:mbt ewstrizontal cord of length L whose other end is fixed (Fig. 6–43). bt,.s m:w c9et
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The p: sge v08kqfbl g5+l8climb is made in 5.0 h starting at an elevation of 2300 m0sgpe8+ l fq klg8v5b:. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator7tqrq.3;zpbhoai /+ 6dz -;alin0ysg 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 move2v+nj/f w6 40evzjt ah 47,000 people per houv+few46v hj a0zj/2tnr. If the 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 rate 766 pkkv)6u. wm6 zdhthvcz,w:- ggbfm- pb.jof 650kg/s and falls vertically 81 m before striking the turbine blades. Cazdhbfu v,zw6p- m 66.jgbctk 7gpw) 6h.: k-vmlculate
(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 coasth4-la 45y hczxer 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 thz-y4xhha5 l4 ce circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could25: a ppf6kk/hxhqo l. convert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by a5o2k l.k6f/qh:x php 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 upwar ert h78sj/ny7y 6vkb)d 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, tr(9lu 1mzdtk4gcln a 98-mla1he 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 t g-nk d l9u8a1rl 1(mm9t4azlche scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a ropbr a qo2semf98, /jq4ke, and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is zerq s8qf/4b jaoe9kmr2,o.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertillt6 jbhq595 vb0 roud+ 2(fmhcal distance of 5.0 m in 9.0 s. What minimum power 0 ohj 9ulfmd6hv(lbqt5 5r 2b+output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped by reve97uprs 7 ,:le evvzua68zao:xnsgs;0rsible turbine pumps from a low to a high reservoir. To rs o;z7:ve0s87u:a vu9xzpl an,g6 sestore 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 sti6uc6,f zspid(8t, 3w2ipolpk ffness constant k is cut in half. What is the spring stiffness constant for ef,pzold 6 pt ,3w2(iku6sip8 cach of the two resulting springs?   k

  A 6.0-kg block is pushed bxrv*gv5w4 g ,x)1h xz7oq1wf8.0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 32nuq1khs8om*cv863x mcd*a o.2 s, how long will it take to accelerate from 55km/h to 75km/h Asscmk63usna1h*q co oxm28d 8 v*ume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walks *hbm (jy px3xln8(ebvje31 6 s.arpo 9on an inclined treadmill (Fig. 6–46). Estimate the power requi8jhxxo *mnb. ypv l3 3( rebe61ap(s9jred 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 fa)yr5/h8 b87jxxpc9cg1 cjwrock vertically upward a distance of 500 m, what was its velocity whe/r 5c1pxb78x9hcjf)wj 8 gcayn 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 wheaolj6zpgp b;2b 2m-rx)a00tu dv5sj3el 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 is it; pua)l mpb6x2b vs0g30r-z jodjt 25as maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s