In what ways is the word zw:gsa54 m rcb 6k(my*“work” as used in everyday language the same as that defined in br(ma4c*y6g w 5zm: skphysics? In what ways is it different? Give examples of both.

Can a centripetal force) .*(errynt mfuwy( .v ever do work on an object? Explain.

Can the normal force on an object ever do work? i944ayu 3;lhrx/co*1oyl3to x uxr 9rExplain.

A woman swimming upstream is not moving with respect to the ssc-n/lzz, 3- e+rbq .nf ow3gihore. Is she doing any work? If she stops swim /,-czzwnrbn i-lsg3oe f.3+q ming and merely floats, is work done on her?

Is the work done by kinetic frictiony dayf1u yf+1 hh9xc/z8wcv-bq/rur y/8 6k ,o forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecl 6ba8rf9qucrfdouy k1y,c1+/vyzx/ -hh/y w8oth out from under them.]

Why is it tiring to ff;ksy 6d (ji:6ef9zvpush hard against a solid wall even though you are doing no wor ;vf ff:sikjdz(e9y66 k?

You have two springs that are identical except that spring l is stiffer than spmd/1e 3f:.o 4yiadfthring 41tfm 3fad y:o.hde/i2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free to slide on a6(-a5emn6xxbtz5 wankix+f o+ z 38ek frictionless surface (Fig.6-30). The block starts from rest at þoni 5 +xxek-5bzw3ka6nta o +6m(x8z efint 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 j+eezv0/hw-e much does your gravitational potential energy change when you jump as high0j+/ vhe- weze as you can?

In Fig. 6–31, water balloop g2i/ze /u 0i;sm/s v)g+rvdtns are tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest sps e vvpgg0r/s2umd+ /;) zi/tieed on impact? Ignore air resistance.

A pendulum is launched from a mi;87 pbwu2a -zsg blf2 22bftpoint 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 t7ibg2 lb2u-pzt ma;bw8 f2f s2rajectory, 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 compre4sg f7lg5xz4zbz e64wss the spring by pressing down with your hand and then release it, can the spring leave the4 7z gxs4w645f zbzelg table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel tfbor a8,j td+lg ,74ym5 ;ovnwire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball agains yb vd a ;njt5gm,o,orlt7f84+t his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy c y2phoaoe; :56f3kguwhen water at the top of a waterfall f3 yagop;e6u52 hfc o:kalls to the pool below?

Describe the energy trans,ex+noc*5vc(8j*ttcjvuek g m 7b)b )formations when a child hops around on a pogo stick.

Describe the energy transformations that take place when a so6 1llcxl vci5hp(.-j kier starts skiing down a hill, but after a time is brought to rest by p c1xl .c5-lhlivjo(6 striking a snowdrift.

A child on a sled (to9 ymkov zl2aug2kml6vr n.882tal mass m) starts from rest at the top of a hill of height h and slides down. Does the velocity at the v 6oz .r8u g2kvllmn2a29 yk8mbottom 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 to step over a falleng eg4t0+0 tyaemb 9aa v,mv(z8 log in their path rather than stepping on top and jumping down on thea y8egt me9vbg(a 4,0tza0+mv other side. Explain.

Two identical arrows, one with twice the speed bw /8ymuzwmg/, rxp-8/qk lj 7of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explai,kyw jbumz/g7w/r8 x m 8-lqp/n.

Analyze the motion of a simple swinging pendulum in terms of energjxm .d3x:s4nd y, (a) ignoring friction, and (b) taking friction into account. Ex.mj sdx3x:n4 dplain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than its or: r6w04mcpbzhh k 6)xofhu//q iginal height? )6o0h4c qw6kzh b/m:ruhp/fxExplain.

Suppose you lift a suitcase from the f8 hc-gp7f,3koah i*ufloor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?ug*8 ,ikh-ha73copf f

Repeat Question 22 for the dkd-6-z; avhza, 8nbv +18qn ecmx 4ts)t0lmlpower needed rather than the work.

Why is it easier to climbbk .k3n ; qjws:c)fbx. a mountain via a zigzag trail than to climb straight up?kwcx: j q;k3..fb ns)b

Recall from Chapter 4, Example 4–14, thbm,0,qn sc) q axigd8)fi*2n kat you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Accouxd,f sb*0i a)gm n)8qknc,q2i nt for this, using energy concepts.

  How much work is done by the gravitati9z51 ::oru ) 7az+dxzykkvh/djyp (jfrzz2/fonal force when a 265-kg pile driver fallsf/o5 ay:y7zdzupz) :z/ k2+j dfxv1(jrh9kz r 2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work ise ss1(k y6wjd1(hu7g u requusjdkg ehw(617 s (yu1ired?    J

  A 1300-N crate rests on the floor. How much work is required to move itm;b-/brzz3 d4:iyd p d at constant speed (a) 4.0 m /;mbriz:yd3bd4 -pdz 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 (horizontally) pushing a 160-kg cratp6hqdicto a1kxs94x, intyp . :3b9r.e 10.3 m across a rough floa pi1thx4bd. 6ip nk3:c .rtysx qo9,9or 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 floor at a rate of forn29 3qwxei 1ar 7.0 s. Find the net work done on the box. 2r aw9nqe3ix1  J

  Eight books, each 4.3 cm thick withg9zfxgij dc++ z o.q+/ mass 1.7 kg, lie flat on a table. How much work is required to stack them one on top o g+ zjdf9/qz .i+cox+gf another?    J

A lever such as that shown in Fig. 6-35 can be 7 xp+o n fg)ti++r/ymgmn.+neused to liff objects we might not otherwise be ablnro++i/n7t +)gfmye. p mgx+ ne 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° incline and is kept fro .lou pa4byolp9e(qhg*u9 db (e.x t1(m accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36.ug*loeq t9a.uo exp (bdp byhl(19 (4). 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 a helicopter of mass M an accelerat ye+* 1phux6*osg2 gjpion of 0.10 g go6p uyp*2+*ej1ghsx 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 axis+dwt nih8g23 cvc;t5 yjl5f8em j 1;sp 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 u5fum y y/emzl(-z17r;. mcvrx axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from xyrvzl;5mre(m. fc-z u1m y/u7=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a particle acts in thunsvt;q.q :./* zn. lslovu8 fe $+x$ 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 ox5k znu geumz2y- (9s gbx07 5q4uxir6zygen molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its speg rxb7hk 7k-p/52xsz cke 7j5bed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop ol0c+esss8pp syx: ex.wv;:kq 0ms -7an 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 1q rjn,xm,o0/ j05km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a)73l tbp1 idpd bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the b)13pitl pd7d bow?    m/s

  A baseball (m=140kg) traveling 32m/s mo db*jd8qi9 iyoet:+(gckhq 2 wre94)hves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on the gqidye2(oh+)e ib8 cr9 9j4k*hwd:t qglove?    N

If the speed of a car is increased by 50%, by what factor will its miaa he;99j6 k:sr0.bbggvtd+ wxa rj5- il *g1knimum braking dtvbk-ekr ;hj.6b5d *a gglgxr91+0 a:w9j iasistance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a levelosr83xsut;8 isow** pk0vr) b road, investigators 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 these data to determine the speed of the car when the driver slammed ob )s*ovui8038srs* ;rwkxop t n (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pit.xvtcpe -ww.g,z/ o /dched at By the time it reaches the plate, it may have slowed by 10%. Negzw..c e,wdg ox/ /vp-tlecting 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 rockl( f 9blwo7v()1kzsu(yfvpp 5 go if thrown straight up by someone who does 80.0 J of work on it? N7) s((vzv1(wko9pl b5f uyplf eglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a singlaco95 hog 9kz4x1fx 4le cablh44zoogx5cal x 99k1fe. 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 440Nelkxz( lb7wqs s4s 0ih;*9k:h/m How much must this spring be stretched to sbzw;: slhie7skslq0 49k(x *htore 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. Whad4 xqg3vk+m1 jt is the change in potential ene3qk+v xg dmj41rgy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter chansdhr .k) df,:vq-n0asge if his center ors0). s-k qdvafd,:nh f mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65p4u+ qos o0pj; 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 the sppq j+04 poosu;ring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from theo2s1sqx osmj/6g1suz65f k m1 ground so it is 2.20 m above the ground. What is the potentiaqzgm o 5j2so 16u/ms xfks1s16l 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 elevati0sse1fhcpd-.m9k :uowvm (2 f on of 1600 m and climbs to the top of a 3300-m vp:cu9mhds kf-f. so20 (emw1peak.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a ruler. The end of the sp90l qy.x97hcfvh jnj(ring 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 up with h0nqcfvj9hy7j xl( .9the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speesiez6 sm;jve2. ,-p bgd (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high m2s seb ,ve;j i-gpz.6can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frict(izxs685 jbcv8:n+zsol( .umwb as 6eionless 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 frict mza7a2f0bdizwqy,r6 p3m *y*ionless 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’p h+iyx r18-xva:9yvas kinetic energy is transformed into gravitational potential-par:vy1 a9i v hxy8+x 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 bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps verticall 9:-qiob+c dxhcj :ok*;)whjfy upward from the top of a platform with a speed of 5.0kj-:jo+hdoq*);h9c cfibx :w 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 const 2wp.4f(qxgqkpst69 a ant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?w p 2(pf9qtqs.kga x46    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction anit) xbpf+45lc.d * s zxrz(y)long the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the toft+*ld)z4z)sip. nx5xryb c( p 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 o5 gqmy/ s4vpj9f a spring (spring stiffness constant k), Fig. 6– j94mvg/ys p5q40. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps fromnp+fes8;9 k, fgc/bol)s+p abnoc h);w+m+k w a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring s + ;8w)fpco mkbnl+bssw/+k9fnh;g +ae,c )op tiffness 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 ca * z xnh*o: zl9u(wm57dcxvl6hr shown in Fig. 6–41 is dragged up to point 1 where it is releaslw vxo5 :zh6nm7d(cuh*lz9*xed from rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at *v/)w -f jtswdqx8+r yan 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 wn1gfsliw hxnsj-;bifri 7 - 2(zx,98 1norg 9a 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 constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass-7w- frio xsf ni8n jnz1;g9w 2s(g lx,ib19hr of the elevator and passengers.

  A cyclist intends to3s5jfx07 qxjc cycle up 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 gph+ju.i6kqkdu3m( 6traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is k d qj6iuhg6km. u+(p3produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the y4n,gzs8r9 9ndaq qe4 bottom with a speed of 2.2m/s How much thermal energy due to friction was generatgy 8eq9 4rnn4,aq9szded in this process?    J

  A ski starts from rest and slides down a 2e twtir:6:l3r:sdw- x2 $^{\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 13.0igvvur.u9+5ng6gi7l 4wc m i. 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 o/ /hwm*: *s,k)rl ljsk1p rclit bounces back to a height of 1.5 m.slk 1,w :m/*rhclr*o)js/pkl
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled acros wq:ob :8mz)vls 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. What is the final sp 8wzbq:o:l mv)eed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passezlg7r+ oc54 tom0-y 9hbjn , rtpr+-vos point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it remg 57-rty vno +-l4t o,p9j zb0crro+hach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steadyhd.3ipahl swm +9 h77i:-iojhskxgfn1m.+x 9 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 sprin2c t.xfmpsnz/h+ .x 70bpfx-r k9bu7u g (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. Whfn b mc/xxp2kp. -.uxz7tru+9fs7 0bhat is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block iwn d(6ns1 /o;o4sp) mu.xisez s firmly attached to a very light horizontal spring, Fig. 6–40. The bw 61s;p/sdo4 o) mneiz( nux.slock 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 beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for th .*vip c6bmr3 6xck/+s 1omnape space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually lanr3 /ni1mvbxa* mp ko+6cp.cs 6ded 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-storywip40 g)b61srta hs/96mzzub window 16.0 m above?sb)1zuiza tsgm r69 /4bw 6ph0    s

  If a car generates 18 hp sww7( /v8iks/ uomk:: trv+avwhen traveling at a steady 88km/h what must be the average force exerted on t+/wk7kirvvv: as 8s(u:w/tom he car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. Whapo l viwa4k98 s.3z:qc; kvb1at is the average power delivered by the engine?k1l3v9 c.z8paq w a;4ovbisk:$\approx$    hp

  (a) Show that one British hors);nnj; -j7,pi 5 diui 8muotlyepower$ \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 i:bhr0dsdn8imy*rj /ugu7 /t9 n 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 d7ib6 y)kbrya.c9 o c( z8f5zjpown from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what pow5oyzp8kc 7 i9yj6 a)f rb(b.czer (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motorzczrv ya*/ 6s( do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter acceler f9z4jg*nb gfhpe )1,zates a 7.3-kg shot from rest to 14m/s If this motion takes 1.5 ,j )hbg4gzp* z 9neff1s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg (g m:2kdw(i4a zo.qcpud (+evof water per minute through a height of 3.60 m. What output rating (watts) m qo((au (zg+.4ev2dcdk w:pishould the pump motor have?    W

  During a workout, the football players at St) ty6-zi7 emd-ku3lmoate U. ran up the stadium stairs in 66 s. The st7mdktu- il-mo e)z3y6airs are 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb u*;*hec p(xt ta 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)gn ds w8)5pvsj4kiw, hill can it climb at a ws4), kdvigpw)8 j5snconstant 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 drag a .vl l. yebx/jqrv*b31310-kg box along a level floor at a speed of 1.2m/s if the coebrel.1yj/ *q vbv 3l.xfficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.08 zlj)h1( l,-tjeqigb $^{\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 carm(w- yrs;pnwo*bc 0/o s have built “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 permanently deforms after a compression of 1.5 cm, but remaincmy;wo (s /porbwn *-0s 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 firs)p,caos)uro 7yb /(h et shelf is 10.0 cm off the ground, and the remaining four shelves are each )prca/ou7( hebo ,sy) spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) ydilliljtnu (nh;6 w.;cs3 ++ in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top ofc(t+uisl+ nh3liwynd; l ;.6j 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 sho5tyzk56 us b9sbb8 d5awn in Fig. 6–39 is to remain on the track at all times, even at the very top of the loopb s9ts8z5ukyad5b5 6 b 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 w e. ms ,ukp10qs/sdp0xithout 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 pmqpx0desku0/ ,. 1 ss78 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 cobpwx /o/.d 8xgd9adf0rd of length L whose other end is fixed (Fig. 6–43 9 /0 apgdx8.fdd/wobx).
(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.j/)el 2 h6zncq The climb is made in l6/hcqn)2 zj e5.0 h starting at an elevation of 2300 m. 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 920isl- khgabu3i5pc:z.7: zpi4n5y0hq -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 California claims that its lifts can move 474/ys 5: segja)3e*rwxhrw t)s,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estim)sw4:* tys ) wse3rhg5rj/a xeate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the ragzv/ so*/kc +g q-n4cfte of 650kg/s and falls vertically 81 m before striking the turbine blades. Calculazgnqg+ 4s-* /fkv cco/te
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vw3c ; vchm*ab-ertical 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 th-mab3vwcch* ;at 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 bar directly into work7t t t)a(+s(kk,rwep o, how high could7pe )ks, takr(t+ot (w an 82-kg man climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward anw-w0w4 u.mh e5vnmuc,gle 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 s le hn8r,x-tk 61i(xsocale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at it lx(ihs816 -t,no kexrs peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a -mki,pa9uxchg(2.q:)m n 8 ymjjxl+d lake (Fig. 6–45). He releases the )q2 . pmua+c,m9jkj ly:-mi xxhn(g8drope 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 h xo fa*so. 6zcp6:wq(p+,nim9.0 s. What minimum power scz+ap xi h6 nop.:ow(,f*6qmoutput was used to accomplish this feat?    W

  Some electric-power companies use water to store energy.)v hr j, )hlbr8yk+xd- Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour b) ,h yrb +rld)vhjxk8-y 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,7db7gxzow . k is cut in half. What is the spring stiffness constant for each of the two resuk.o7,d wb7 zxglting springs?   k

  A 6.0-kg block is pushed 8.;lli1n*,mn av 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 du8: 4t qb5zf*waao3z55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stay 3:t4*oafwzdq 8za5bus the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”)jf-unbi;j6 ezc- b z db(bk-169qp c-y, the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient whef -kij-qu dbcyb6cez; --(jnpbz 9 6b1n 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 c 8i0ng3(n-j, bs) z1xsff,ygi)lkpw 500-kg rock vertically upward a distance of 500 m, what was its velocity npn8bl),0f(i1f3,sicz w gjsxy- k)g 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 height of 2.0 m at a 44t cj0byp+ frnt lq2cf** 9oirate of 95kg/s (a) If this water wheel is set up to 0tytn4i pq4 ocfc lb*f*+j9r2provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s