In what ways is the word “work” as used in ever3mui6mt jr3s s.zkb k8uc7.b4 yday language the same as that defined in physics? In what ways is it i.4mcbutmb 7k uz6j38 .k3ss rdifferent? Give examples of both.

Can a centripetal force ever do work o3ncrzw 8or6bt/6n5 n bn an object? Explain.

Can the normal force on an object ever do wor(e 4y9-+wz+kff igau gj:s dq9k? Explain.

A woman swimming upstream ).9uv7 ec u (k+:xqbpnyyc8cyis not moving with respect to the shore. Is she doing any work? If she stops swimming and merely floats, 89xq7 cu)p:c(.eu yyvyc+ nbkis work done on her?

Is the work done by kinetic2(y4 0qqo5c -bgoqrv6mbz+ho friction forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth 4 o gqvmhybb-6 r5(+zqcoo20 qout from under them.]

Why is it tiring to push hard against a solid wall even though you ardo04v0m/,i4ccq q*3c ry c bgbe doing no wov/y oqc04 c 034cmbcqgdb *r,irk?

You have two springs that are identical except 6y/b9ne+isp6 q7uayr that spring l is stiffer than springr6u 9ynaeibsp+7q/ y6 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 horizon5v(xdho 9 (lkxtal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from(vh59dko(lxx 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 potential energy cn2c0udd 4/bu lhange when you jump as ucd042u /bl ndhigh as you can?

In Fig. 6–31, water balloons are*z +j aw -ouin(dxqi0y213rrn tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speery+rx (1uan02 ji-z wod*qin3d on impact? Ignore air resistance.

A pendulum is launched from zv7x +o:s iq:2hxfl ngdij)l:dw 5x/ :a point 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 launc:l:vnw:7 x sdfgx xqiz2:j/i+ho5l) dh, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress the sprinjbt 7 c1en6vx9d2c2 jrg by pressing down with your hand and then release it, can the spring leave jtcdvxn9 61rcbe7 2j2the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The inst8i1ts k2 ix ttktl),gq,.yr*tructor pulls the ball back and stands against the wall with the ball against his nose. To avoid ii)8lt ,str k.,gk1xt 2t*tyiq njury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top of a w m83ntu+zm.q 46pqcqnaterfall falls to the pm+pcq6 8t.q 34 nqmzunool below?

Describe the energy transformations when a 6g: le:*glcp6pys41x. fjo lw child hops around on a pogo stick.

Describe the energy transformationmmmtle 3w 45)t(w /sy56pufax s that take place when a skier starts skiing dtw 6y p)(xe sw4/utlmammf553own a hill, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hit,kr+d1b3meekx 3m 7 z)yxt4kll 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, aktzexek btm1y7+3k)mdr 34 x,nd (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in th mb eyxlcd::0/eir path rather than stepping on top and jumping down on the othebclyxe/:0 d: mr side. Explain.

Two identical arrows, one with twice th)dw,s wl ;ashtj;.u2de speed of the other, are fired into a bale of hay. Assuming the hay exerts a2uwh s);dald ,w tsj;. constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a sir 3pm 8(/pdweckd k0l6mple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock hasp8k0mcew 6rl3 (p/ddk to be wound up.

When a “superball” is dropped, can it rebound to a height greater.idry k t60lz0 snv/+j than its original heightj+k.lyi0 0 r6/tndv zs? Explain.

Suppose you lift a suitcase from the floor to a table. The work yoaopwc lc:+:cq-quwktzb1tomt4r1 j,4*(m l2u do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) thctkjucot-r(qq1b4aw ,p2tolm+4 1 l :*zm:cw e time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power neecov*rs0 /n3ww ded rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb st0b5,ea )k(yv / hsdkairaight upyv/)(a kda 5bekh0is ,?

Recall from Chapter 4, Example 4–14, that you can use q/)hex4u mj0ka 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, how much rope must be pulled up? Account fork0j4/ umq)xh e this, using energy concepts.

  How much work is done by the gravitational force w6dzs,)/*h2 yrcz *j :j1b wako)) l(btegkejahen a 265-kg pile driver falls 2.80 m? zt,l/6b1:j d*hkoreae)c w s*bj)zkg (y2a)j   J

  A 65.0-kg firefighter climbs a f9g+ wz pi,xkj-kiq 7b;:xewd0light of stairs 20.0 m high. How much work is requirqpe- bw :xi;jw+ 97kgkdzxi0, ed?    J

  A 1300-N crate rests on the floor. How ;tbl )egwc*p1 much work is required to move it at constant swt)p 1c; gelb*peed (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally4:6 1eyrgbrlp23 tyh b) pushing a 160-kg crate 10.3 m across a rough floo1bl2r6 htb3 4yyerp:g r without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a fl- i3bppg3 d+hgoor at a rate of for 7.0 igp3 phdb-3g +s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. Hovu *lhn v1n c ptkha6 z9(b)(wy/lb-7q hxy+d8w much work is required to stac8yp(cx khq1lnlzh*)tbh- 9 (+ udw/7 nav6vbyk them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be usedhmj u;v.9.by4 bcl7 mtr g1mv: to liff objects we might not otherwise be able to liff. S7hvmlj41 u g :9 ;.mrvbtyc.mbhow that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from a*qu w6m gbg+yw*b(lz2ccelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The ef+lu mz6g(y ww*bgq 2b*fective 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 anj m7 u-u1dzb.g4 (pbjl acceleration of 0.1bgj1u 4d.p lz-m 7b(ju0 g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance axi, *n yrw0e1uu9cp;szbs is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shown in Fig. sd. vmq dv(( gsr-ncoc, v4,z76–37. Determine the work done by this 4 -vo c svc(vdq,rms(zn,.d7 gforce 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 onz+ p 1os80cjmy 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 mole8d oac zcjqg4t)-l/9u cule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its speed increased?jq; (v jsznu3,9ou3 ub*cq9o w $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an el.0xo 3ifm4ea-o iu) jqectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 bee,gcb78 lav. w+hw0a;f id tx1 /s5go6tj n/sc done to stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an averag+aqz q b -gapk/i9x:fqt( 14nxe force of 110 N on the arrow over a distance of 78 cm. What is the speed(tgax+f/qx1 ni:qakz9pq 4b- of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backwfy8 gntf36kl*6b v2 ysard 25 cm when the ball is caught. What was nvl6g s*3yffb6 ytk 28the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%,.7ivk +-ajf7,zsk ury by what factor will its minimum braking distance be increased, assuming all else isi+ ufa7. s -r,zkk7yjv the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s sk x2u z.ui0h)y -g:p) vcaobsq/dfd5bb3n-bg9 id 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 theosb2u i)ag-pzb :c0 yh3/9qbnbf)x5dvdg u-.se 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 time it reu l17e;2 u nvi)we1pi 6(zhvnkaches the plate, 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 an)zei1ln ;hvpu2(16 wk ievu7bout 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by ssd),rn+3 8*s oqyoclfomeone who does 80.0 J of work on ir qo*dsys) lf8 3+,cont? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a sinrw x. 3fr9uj,f1ft7 i5lxmc.erf ;j*sgle cable. Deter5ricf1*fux;, f.temswx fj79 r3.rjl mine
(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/mv:lgygmqy-*b f-jy z/.3.cs p How much must this spring be stretched to store 25 J of pot.3p. /c-g -*yvmlgsq jbyzfy: ential energy?    m

  A 7.0-kg monkey swings from one branch to anot4whx .gwg+u.6 ubs2o ther 1.2 m higher. What is the changeg ob+us wh x.t.62gwu4 in potential energy?    J

  By how much does the gravy s.8zljp(3j* f .ggjpxzlb6*itational potential energy of a 64-kg pole vaulter change if his center of mass rises aboutp 8zgzlfl 6yg*xp s3b(jj. .j* 4.0 m during the jump?    J

  A 1200-kg car rollingvp6(9z,:rurv pdk mfq65/ f9ygxwj4c on a horizontal surface has speed v = 65 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 constant of tug jqcmfw95,(f9vyd6 rr:pz x/ p6k 4vhe spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m abo yed3htst0z,y0b:b z0ve the gh30 ze,y:tybzb0 dt0s round. What is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs to t m728t/ne(ooq9w :etf1 cmquihe top of a 3300-m peai q9utfc(e m7o/t8 e2n1mowq:k.
(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 ver-o b9t s*knqmpgtb28: tically next to a ruler. The end of the spring bs8-2 9nt o:mbqpg k*tis next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is ruk+0z 4qsutgv7 nning at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upwar4ugzsv70tq k +d?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionless m bii(gp18ds;35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frv9n r(eta 8q(kictionless 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 r0 zuj1muhk2r rdpub 78f )b2/kinetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in obrr k) mr7u8jdu2b0hz 2pu1/frder 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 3p 5jt -*b(p) tf7+bfepebj vmvertically upward from the top of a platform with a speed of m-t57fvj(btf+e3eb p )p pbj*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 spring stiff94* vj. z;qw a+fgchfvness constant is 950N/m is attached to a table and is compressed down 0.150zfwf;jq4 9* .gac hv+v 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 lpf32h (0abiu iw hbi3u.oh/2kooped track shown in Fig. 6–39. If the block is to remain on the track, even ati3i u20 3k wapbh/iuh(fbh2.o 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 st l zsnbs*q,+* 2grk4cxiffness constant k), Fig. 6–40. Thesg z,nq 4cx*r lbs2*k+ 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 bridge. She is tied to a bungee cord + jokv/- dwh )yfn*2tqhblm,a(2y- urwhose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the oj*- vrhyu)dh bla y( m-f,qn2t wk+2/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. 6–410uaz)aa9m ,nx is dragged up to point 1 where it is released from rest. 0aum,aa) nxz9 Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed ofap /4gc7s ui onn/u/e6 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 bottomyi eyy*)+qk qf1yf/s* of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 gf1yyike*q y)+ qys* f/ when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up6n m5t; *byvcd 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 kgvf0juf9 +iw( d*5qt fdwfs,ee*0/ sef and traveling 95km/h in opposite directions, collide head-on and ce5wi+/ f,0 tef(qdf0s** dfuf 9eswvjome 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 reaches the bottorx* f955 g1lp ; ltrcbibrghb1+dxh9)m with a speed of 2.2m/s How much thermal energy due*5hrb ixb9xd 9cb) rth1f;+l5 l 1grgp to friction was generated in this process?    J

  A ski starts from rest ak2-ex .06m 8s y7pssarsm ufmsb m*e2:nd slides down a 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,l(w,y5yh ;r0 gaiqlp tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back tqtj8demjz81m h/w) (. 6rwgxb88 mexyo a height of 1.5 m.)q h1/mx tgwm8e 6(jx88w8djb m eryz.
(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 :f0mri 8f (- ;s.slbyjnn kt/dfrom rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for dyk/ni(t ;f8 b .js:ln rfs-0mthe 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– bya*3(u*89 xg(r tvhs flv3g*. hngmt41 passes point 1 with a speed of If the average force of friction is equal to one-fifth oftsv*( *artg(8nm y3x3 g9lghf*vhb.u 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 5/b flc 2yf0b(sxgu2rof 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 tb2aatr7k6:7nqt3xnattached 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. What is the coeffi taxaq7 t6r7kbt:nn23cient of kinetic friction between the block and the table?   

  A 280-g wood block is firmlyfnvu 0+4jmck 6 attached to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyonj4ucnm f6v0 +kd its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” / /hn6vya7v;aj gngm -(mass of 980 kg including pilot) that was launched horizontally at 500km/ma n7v/hj-;ggn6 ay/ vh 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 a 1750-W motor t u csit,2i8v/to lift a 315-kg piano to a sixth-story win8cvti/2 is,t udow 16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h wlj.y6baru 1;)2uuhq xhat must be the average force exerted on t) uua6q.h 12xr yj;ulbhe car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is te3r n +b+b j 8clejeu.x.i/nq1he average power delivered by the er e ujl q/x 81+jbei..3+cnbenngine?$\approx$    hp

  (a) Show that one British horsepowe+,ewskfce7bbr :/ 1h fr$ \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 o iuk owx9b40u kmse85/t( u-xew.j(dzf “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 down from to 65km/h in about 6m.a0peg 64xpv/ dtt1u 1a,mvf .0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a cons /g,tpam.pv txf1a1ed4u 06 mvtant 75km/h.    hp

  How much work can a 3.0-hp moto) f-d,qezjaa4 r do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s I de9ck9w73r 9qcsl-l rwr 2c)ef this motion takes 1.5 s, what average power was developed9 rcq)-eskew2 clc3997rlwr d?$\approx$    W

  A pump is to lift 18.0 kg*da0: yy dfs 7zs3hmj8 of water per minute through a height of 3.60 m. What output ratin*:0dd7 z8 3safjms yyhg (watts) should the pump motor have?    W

  During a workout, the footbal5;.keanql2q q05 ktwdgj5 3+2 ycdj fsl players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an angle w2g;2q t 3snfdq+cj5 lje.50qkyad5kof 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 +o,h tz u2d1sla 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 cjnfa-2 n:scw lqn51 x4an it climb at a constant speed of 75km/hcn -s24aqfn:jw 51n xl if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have hlf3g sv,)me07ikhu1 to be able to drag a 310-kg box along a level floor at a speed of 1.)ukm7i0es fh, 13lhgv2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dowi 2 fd5j kco8w8(hy;oin 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” that arexjce 7i 7+1x ca4wdo5s 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 1is eax+j7ox57wcc d4amming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cb2u9 n(wdkpd xpi+83bm 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 pd+x8p wb db2( nuik93books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jdrjs2))x ffdki3 sf )5ump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch poid f2is3rj)f))xdks5f nt 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 tra8a-k:h-k woiqoga*f (ck shown in Fig. 6–39 is 8a(ki qhk oa*-:f- owgto remain on the track at all times, even at the very 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 jump:bo wm-+glc*g qrxiinnc0-*)ing from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and hi-g qwn:* + o)*gcibmcn i0-lxrs 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 other end is fixed (Fit- vw2hj rjf6(m;fa-cir x7f3 g.j h mvw7( cftr-f-ar6x 23f;ji 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The climb is made i-z q6,q7txa tan 5.0 h starting at an elevation of 2300 m. Calculatqt7z6xt-aa,q e
(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 elevator is 28 m a; qzt9j/u h wk,hsxlgp vki3q10,nzbvu u*:0+bove a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 47,mg-*-ohja/ed 000 people per hour. If the average lift carries people about 200 m (vertically) higher, esti- */eadhgj-m omate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at 9*b7y3dukqrtli+jz4vh *3 ji the rate of 650kg/s and falls vertically 81 m before striking the turbine blades. Caz*33i dlr 4*jytvhq9i+ jbk7ulculate
(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 z(xhg j0 m 0s c;th0vqlbin:9*with a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the boz s9nh0x 0*ic( lqgjh0b tm;:vttom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy m;9 gjq8kmc nmkr.s0cv f17u:bar directly into work, how high could an 82-kg man climb a laddernj9k0rfu 8cc.v: m7g;sqmm k1 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 upwar0ffyw)67 j1msz rx9qi 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, the spring insid p6 q:7my;cxn4*dtagxe the scale compresses 0.60 mm, and it tells ndm 7c;4qtax gy*x:6p you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m pxt.fut+/4s k/s grabs a rope, and swings out over a lake (Fig. 6–45)tf4/p.u+xtks . He releases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m in 9.0am9n z2qb1;0 wup;kn c s. What minimum power output was used to acc9nzpw cumnk2q1;a;0 bomplish this feat?    W

  Some electric-power companil;xw +wu(hnm n(f08a h0l*ivm/:sxm kes use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0khxw *hn s+f0/w m;(m 8a0(imxlvunl : hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut ,nx( ozw-a td6hgb+;bin half. What is the spring stiffgz-da (boxthw bn +6;,ness constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a/903osk2ern5;cmyr4tt1 eb)w dw s dw 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 3.2 s, hoj0 8wlowl 1(botrhomtif90i1q1/ h z3w long will it take to accelerate from 55km/h to 75km/h Assu 1 o hh(8m0iwollt91 /3zti frwbjoq01me the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stlbfvbt3c j bu/0w;3w) ress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmiu/3b )wcv ;fbtjw3bl0ll 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 ) x v/5yuzyfa/a distance of 500 m, what w)vxu ya/z/ fy5as 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 wheel from a heig,xcfxs7h3ge ( ht of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maxh( gc,ef xsx37imum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s