In what ways is the word “work” as used in everyday language the same as t.ehg84/hyuei 77nvxr;3ap prhat defined in physics? In what ways isg urp3ynp;h7a4/8.veeihxr 7 it different? Give examples of both.

Can a centripetal force ever do work on an object? Explain.qhzj,d -88xmxt i,94 vp;setq

Can the normal force on an object ever do xzb.x;kvkyp6hk.:. r5 i0uwa work? Explain.

A woman swimming upstream is not moving with respect to the shovtavz:j0 s0. dre. Is she doing any work? If she stops swimming av da0.j0:zsv tnd merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consider whapdy9;d +x,5ynb 3nvot t xyn;vnp 3d, 5b9d+yto happens to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid walal,g 1f(a-2u hfsz;pu4xfj8 nl even though you are doing no n 1hagulpsx8(u jf-a;2 f4z, fwork?

You have two springs that are identical except that sprinhbr3l )gu *ry;g l is stiffer than spring 2brrh 3u)gyl ;* $(k_1>k_2).$ 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 horiseid 8 tst96)d (zf u+mg7yh a8;xol 78oi2puszontal force on a block that is free to slide on a frictionless surface (Fig.u2duoflz8th69oxg8)+ds ;e( s8 p tsi 7ay 7mi6-30). 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 poth9 :/9rnm dfi *,hingfential energy change when you jump as high as* md9ni n,fhfg9:/hi r you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, a r-;jtqd *oxe3ll with thex*;oejrqd-3 t same speed but 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 height h above its loweu4lakz.xtmdorl, p)) aqf26/st 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 ukmo6) ft4a,q.u d2a pz)l /lrxpward 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. If6k.ujsfqm, -k8 1glj q you compress the spring by pressing down with your hand and then release68-jm.q1fugkqk, sj l it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The instruex4fv/ gi, 3tnvic31o p gn1;wctor pulls the ball back and stands against the wall with to1 4f3 i 3igev1n,/;vpcngtxwhe ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy wheq gemodf ; l,g/,tv7:on water at the top of a waterfall fallo g,:emqtlo /vd, ;7gfs to the pool below?

Describe the energy transformations when a child hops around on a pogo stickh9k7jgqvygr+djy ruyoi;:4t.(68 kg .

Describe the energy transformations that take place when a skij8q -zz hg.7kfer starts skiing down a hill, but after a time is brought to 7hz-zj8 .kqgfrest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the,jthx( tb y8;(( je7axtc)xv)clnk c, top of a hill of height h and slides down. Does the velocity at the bottom depenh y7)xj)8x tc,t(,cv;(at kx ebc(ljnd 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 to4mz.y.ej 8tku step over a fallen log in their path rather than stepping on ty4m.u. 8eztk jop and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other21o-j q84ly wlvq)4k* xnzlyw , are fired into a bale of hay. Assuming the hay exerts a constant frictional force on thezvj1 olq4qy nyw 8llk2-4 )*xw arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pe* /ucgv);lwjix /2vpi*o7cc p)x8gwo ndulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfatc7 gp iu)/*v8w )i*poo;xlcwx gv2c/ jher clock has to be wound up.

When a “superball” is dropped, can it reboun6.wjahd5sax20r9 8w;xor m rf d to a height greater than its original heighd2x9rawra8 0 jh5 x6f.;wrosmt? Explain.

Suppose you lift a suitcase from the floor to a table. The work you dgz/ ;rji1p ;cpo on the suitcase depends on which of the following: (a) whether you lift it straight up or along a c zjpp;i1 gr/;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 workmy5 hhph: m ptbr xyj1(l.v(pf.h/0d)8oya7p.

Why is it easier to climb a moun5k)d pk us ecsm23ajgqw+u.-u.7 e ;qftain via a zigzag trail than to climb straight up?)j+wdu aeqqksg 2e 7;s. 5.pukfc3 -um

Recall from Chapter 4, Example 4–14, that you can use a pulley and p hd.fettpdbsci( 24-n2)xtw .ij6:b 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 for this, using e s tdx6 -2pje t:nh4.fd( b)p.iwcbt2inergy concepts.

  How much work is done by the gyvlgz4w+bg5 ,t qnc up;1+i f1ravitational force when a 265-kg pile driver falls 2.80 m? y1fw4 g ;qg+bipnu+lzc,1 tv5    J

  A 65.0-kg firefighter climbs a flight of stairspdzn6cxm-/ 3cf z(5 gw 20.0 m high. How much work is required5 - fw6zzn/cc xpd3g(m?    J

  A 1300-N crate rests on the floor. How much work is required te gv:/n.vc/umxg:rybc w t;2. o move it at constant speed (a) 4.0 m along w:2r./c/g v ;txbecmvg:.yu nthe floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally az/tpx2g2epzb ;a98:etf -ak) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effect-aeztb9 kf e228zpgx a:; a/ptive coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a7e93nxvlkq 8a 6de:bdxd/+ b l floor at a rate of for 7.0 s. Find t 8 3lkbax d+dvxeqnd 9l/7:eb6he net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. H9,e1 v9tb ,p8 y:h0exjrsomjiow much work is requi spmh:oie 9bv8eyjx9 1trj,,0red to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we mi 6ywa0zix h;a8k ba:+mhibbx.- pi65rght not otherwise be able to liff. Show that the ratio of oba xa+y 0w 65mi; ix 6hb-.pkbh8i:razutput 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 r 8wdfgva)9b*xu,zs0 ljj - 0d3.6 m down a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the inclid bjlzw,)ju0d9-0 *fax rgv8s ne (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M a)ro* mp,b iso+n acceleration of 0.10 g upward)rs ,omp*o i+b.    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 ax (. 32o pkl7hemno*wmlis 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 )hm39 evi*ws(wut. xjx axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m (s9*3hiwv .m wte)uxj 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 iq;)e scqrk 98ncj 7v*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, 3cikd)w qy406 skeez/ 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 ipyj+4oiy0,th s 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 an electronr/c3p:b r(*n0 0edzpzao t d9b $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 xl j9smwaqzui 1o1 uuym+12 o45s5 zb+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 average force of 11y75(p yxf0d7qxob ) mi0u9 nnl0 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leavesd5noyub 0mn079 l7qi(yxx )pf the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backwarfh -vvyvf 4p1g-i nsz4 l9/l-fd 25 cm when the ball is caught. What was the average force exerted b4 fvl1gi/lyvh-- fv s p4z9-fny the ball on the glove?    N

If the speed of a car is increased by 50%, by b nl 7u)km7z 8*oaqgdj orv2*0what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the dri*zo g287jul okvq*b)d0 r7amnver’s reaction time.

  At an accident scene on a level road, investigators measure a :(lisvmmy-k p:3/pl i car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coeff /ym (pmil-ipks:l: v3icient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitvm-*svp tv)mu2x ff*/ ched at By the time it reaches the plate, it may have /ff m t2vmv )p*u-xv*sslowed 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 thr (*g/f4q gnbdxa) g (v4gqrnl2own straight up by someone who does 80.0 J of work on it? Neglect air resistgg /d (n2*avlq44r()f qgx gnbance.    m

  A 285-kg load is lifted 22.0 m vertically with an accelej 1blz ui:9md+ 8fat9j,ly6 zpration by a single cable. Determindz+ji8lu mpa 9 lb91jfz,t: y6e
(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 stifsu5heev duj185j92 cqfness constant, k, of 440N/m How much must this spring be stretched to jd12 9vj5eh ce8uu5qs store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branc8axc wo3ag /4uz0rce:9w0 hxv h to another 1.2 m higher. What is the change in potential e z8/ogwx:093 0cavx4acerhuw nergy?    J

  By how much does theh+b42cu+t ek6*awew n gravitational potential energy of a 64-kg pole vaulter change if his center of mass riseswnw6uct+ +2k e*4aheb about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface hqrc.asv5pm,g2 ,avf3z7) ysl as speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of y. rc)p2,lf3 s75mvv qzgaa,s 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-krfx623cn 8y+ b q;uv, )kbqoysg book from the ground so it is 2.20 m above the ground. What is the xoqkyq+ ,6vbfn r b;u)2yc38spotential 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 eleva (pxua6nq2 k,ction of 1600 m and climbs to the top of a 3300-m peak,uqca x(p26nk.
(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 sprisw5;oq 7ezg. 1ae4i uhu6r9u t*jk)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 s* a6;g1r9 uq.s4e ihwt5 j7uokr)e uzipring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzare wqp91+cqr0:c3j*kc59flxk t/ huin, is running at top speed (5.3m/s) and grabs a vine hanging vertically from a tac/kq tlqc9j * fhpr0kc: w 1r9u3+e5ixll tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slide:ly4bfuvpi yx;4; 7-2w kz lfis down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frictionl-6ufex8 2cjk less 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitatioft5 t+it ms(n*nal potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a sf(nm ti*t5s+ tpeed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps verticall9r d /szzcxh37y upward from the top of a platform with a spee/h37zdrcsz9 xd of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignoko :8pd0y vc,mre its mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can itm,dpy:k8vo 0c 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 loi,,tfw9cwsoob ,l*)f oped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must i9i *cbwf,olwstf ,,o) t be released?    r

A block of mass m is8q +/h(5 ulgy 17erjxcyw6llxa6 fb w- attached to the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initiw/j7hwqx6 ulc-f el5y1r gbx l68+ y(aal 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 jg b sjk)p-/yf )./dtmjj .o*ibumps from 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 stiffness constant k of the bungee cord, assumb jp/ *g).kmb-jfyj st.i/d) oing 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 dr/yy3q h 0q rb4wbfov2(glu*(lagged up to point 1 where it is released from rest. Assuming no friction, calculate the speed a2vblg3 qro/y(by f(4 hu*lq0wt points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speeig86za) i89+- fev wezpx:bdjv-/fy gd of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be abiz9s 3n )ro,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 whenir, 3)z9snabo brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends tou/a,z vddtx,c3gn s63 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 hu:lpy9bagi,9 i38v sof mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much theu3 py,il98av9:gbish rmal 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 t hs2d/e6f0 v)uvw n9yahe bottom with a speed of 2.2m/s How much thermal energy yvsenu6/d02f)ha9wv due to friction was generated in this process?    J

  A ski starts from rest a1sa/n3dk4j9r (v a hjlnd 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 tree -q,tqkuib/cm 7uzy-113.0 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 i/s 0 c0pxbdy8e ohg-5i:)knz;h;e sikt bounces back to a height of 1.5 m8k0sg ;k /ceos d)xpnie5yhi-z: h;b0.
(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 fe ,w q1ox5zrt:rom rest, is pulled across a floor with a constant horizontal force of ,z1qe r to5wx:350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coa3/ r+u fgzg+j:7ep eqvc,x*aq ster in Fig. 6–41 passes 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 reach point 2? pg ecxfqj *gr,37ze /+vu:+qaThe distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady vi6 v y8(/jpxdk/b )fkupward 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 b3:b(vdz ofh ;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 coefficient of kinetic friction between the block and the table?;fb zb3:vo(hd   

  A 280-g wood block is firmlyo7 (fgzf9drh 1 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 beyond its equilibrium position will it stretch on its fid fgrh(o179z frst swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg inclu8*urg9jalv..ry4; ft2. zwdl odn b/t7, ntytding pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What y9oz.u afttwn. 4,jy7rv2g d/lb; *n ttl8rd.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,rlnmfwdop (2)flj 2*z:v0s oe ; t/kd-W motor to lift a 315-kg piano to a sixth-story window 16.0 op2m0 *wtl2ovkz/l:dff nej( d s,; )rm above?    s

  If a car generates 18 hp when traveling at a steady 8( b32udi obyigoyz1st/f0 ,cr5*o;m a8km/h what must be the average force exerted on the car due to friction and aic*u/y0b 35dg(y zao2 tr1obf i ;so,mir resistance?    N

  A 1400-kg sports car acceleraa h .mysk 2i/m afdhzfzf7/97*tes from rest to 95km/h in 7.4 s. What is the average power deliverea79y *mh fm d2if fas/kz.z/h7d by the engine?$\approx$    hp

  (a) Show that one British horsepowefixxo1yd:.4fo4tonejz04n (g o f )8or$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “ki qlvs1)8pvj: oil4lf.lowatt-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 from0e *u i*/pr0 vh-btn:nmvmr3l to 65km/h in about 6.0 s on the ler* v 3/vnb ln -ummr0ih0tp:*evel 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 3.0-hp motor do (ilw n64n (jw 7hgkf heytx0)-in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest ttks1j+jp t00xt hufkr*ok jm04(f:r8 o 14m/s If this motion takes 1.5 s, what average powxjmkuf rhst j0j08+t0( *f4k1:t kproer was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a 4 0kl,i-d 2*yeh. umaaylnrz7height of 3.60 m. What output rating (watts) should the pump motor hav0y*4r ,. nlk d72lhe-ma uazyie?    W

  During a workout, the football players at lo5jsfxtb;;a: s.;mulj92r qp 5rh7c State U. ran up the stadium stairs in 66 s. The stairs are 140 m lo.joh 2qfsrt9 pl;:cb;ju;5a7 mxls r 5ng 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 . xgmuxgqt5 -2xko9t.i,o+wxa 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 maxil vk3uy:6b,z cmum power output of 120 hp. How steep a hill can it climb at a constant speed of 753yk:v6 bczl u,km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag aqx)8r2evwit m7* hl-t 310-kg box along a level floorq-mtrw i x*tl7)h82v e at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts downc3s,:ie+x )wn*srysg 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 ha2zj8 gy *p0aue 3g7i*8agkkoive 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 remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has ga*i7 yjgo kapuk3gi 80* z2e8a 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 is 10.0 cm off the ground, and thej1 m7i(pirt 22op7su5 xs,fky remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the flooo22 1 ,57mijfpsy ikurp 7t(xsr to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fiok8fb(ss ls4 fmm:zi 2t b9 +1evq9,ieg. 6–42) in the 1936 Olympics 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 he was traveling at+i 8oe:(2ms1b v9bmkiftq zl4fe ss,9 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shown r3 zl(t)m)vks (atqg/in Fig. 6–39 is to remain on t( sz)gmkt a(v3rtq )/lhe 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 jumping vmtitejvw v;o;ia4z5* gb7:6 from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived w 5gi ;btv*ei:mv7v ja4;zwt o6ith only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whg:va/j6h 7peqose other end is fixed (Fig. 6–43). gp:76/ha qjve
(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 mawl d0f7k:k7+tksn a; d vsk0q;de in 5.0 h starting at an l0dw s; k7kf 7:dqa0 n;vkks+televation 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 920-kg el,r 8/yexx47.soj mfkm evator 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 47,000 peop,mu vfn2a9) ghle per hour. If the avevnufm) 92hga, rage 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 of 650kg/s and fallsz4m ra 7+5bzogcxc ehe.z:3 4x vertically 81 m before striking the turbine bladesx5 :.3b4o+ea7ezcxh rgm 4cz z. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a.xb n ;px0y,dj circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, thx0 d;xp. j,bnyis 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 barhyu 7qr46. anr5n zzzd1:(r8ttm, uop directly into work, how high could an (17ttr 4ryzhuuz ,o8 nzpm6r.d5:an q82-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 n.*wb)k( x9x jor0a:i bbgcr;an upward 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 springnh2d*b.pe j,vi 5f em yiy*,0(bha2pr 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 hbmhephy, p5b ,.2*f2a 0* i ndejrvi(yeight of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (zbr 9rne p-ujooi3+, c/amg4rp9; h8nFig. 6–45h9roi u jo+ne-c9rpn/ra48g, pb m;z3). 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 ofmq8dsa uv 431d)6 mdqs 5.0 m in 9.0 s. What minim)qu6 svdd8 1qsm3 4damum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. bo; gdt6ow0 t*hx ct9qm,:am9Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hou: mxtmo,9b*dq och06g9;t watr 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 isr:(i-kir/vo vo4t .eukq 2+xz cut in half. What is the spring stif2oox.:k-v qiutz k4/( r+ irvefness constant for each of the two resulting springs?   k

  A 6.0-kg block is pusheajy q17ug)apr r4 *jeh93 ls*hd 8.0 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 3.2 s, how long will q)1t4u:fw z uvit take to accelerate from 55km/h to 75km/h Assume the power stu4z wu):ft1vq ays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the paqm.2 /hvx: blatient walks on 2l axq/h.bv:man inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upwa ct;upq e7tn1u :v(df5rd a distance of 500 m, what was its velocity when it left the volctu5v;:q e n17p(f tucdano? $\approx$    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 wat*ccbyhi( xo9t /bs gr n0c7d70er wheel 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 idb7x(tgo bc90ry0*7h/s inc cs its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s