In what ways is the word “work” as used in everyday langu: rfjnl.y 8uz,age the same as that defined in physics? In what ways is it different? G , fn.yul:rzj8ive examples of both.

Can a centripetal force ever do work on an object? Explrkrk cc51:0c/hw8kcrain.

Can the normal force on an object ever do wo2 u,77r +u nad-njk/rhbt5csw rk? Explain.

A woman swimming upstream is not moving wvhws bqteebe 5inkt.rsl ,8/fp5(24 7ith respect to the shore. Is she doing any work? If she stops swimming and merely floats, is wo4wp/le8svtqkrn5i h etb2(7e. f5sb,rk done on her?

Is the work done by kinetic fricpd q/4bbykr*4 6c) ieition forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from under them.]4i d)y*4reik6b qp/ bc

Why is it tiring to push hard against a solid wall even though you are doing no jt.g-zf qe:3q work?z qj.get:-fq3

You have two springs that are identical except that springaosvb+ g6lz/i:c(6zl l is stiffer than spring :(iozvb+ lsac6l/zg 62 $(k_1>k_2).$ 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 a0i b*in mr39uk10tvglm q/4dq frictionless surface (Fig.6-30). The block starts from rest at þointb*lvm109iqkdngtu 3r i/ 0q4 m 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 gravitationa95 yt sx:+ooc*noiih+ocd7 i;l potential energy change when youhotn oi ico+iy5c97sdx+ * o:; jump as high as you can?

In Fig. 6–31, water balloons are tossed from the roo8l- n* 0 pmfhxwu23pvef of a building, all with the same speed but with different launch anglewf-3pemvnh*u80 x pl2s. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a p;nu:v *0kqlyooint that is a height h above its lowest point in two diffyl*;novk: 0 querent ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a:ua 3,hviwlna dw2 64u table. If you compress the spring by pressli 3 au6hd4:nw u,2awving down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceuy+r5 8 f9qrfkiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands afkrf985ru + yqgainst the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy whee;;ipf pzho9 ;fg1keyig/-:r.zhbo6n water at the top of a waterfall falls hriz 1zg.ygik:; peb-o 6/f9po ;hfe;to the pool below?

Describe the energy transformations whenwystby8j5pp ak2wx jz q:;4 ,qzjxut2*2s t8( a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier sta5uo1q(: c5dzt cy 1tbtrts skiing down a hill, but after a time is brought to rest by striking a snowdrift1o 5td( :uy t1tcqbc5z.

A child on a sled (total mass m) starts from rv vmt-/4r9pnrszc4h9 e) 0h qnest at the top of a hill of height h and slides down. n tv4q4cens v)/h rm990rhp -zDoes the velocity at the bottom 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 e ;(-afcbgd7, hkkkp)to step over a fallen log in their path rather than stepping on top and jumping down on the othkgpebfch(k,a 7 k )d-;er side. Explain.

Two identical arrows, one with twiaq fnrk ijp(sk5h()w:*r ,v 4yce the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows,r , pvkrk() snfw(: yqh5*aji4 the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swingi)lw lnouyyva : ab441/ng pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explaiuyb:w/aon4al)14 yl vn why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a heipmt ( 7+0hdmjyl)u,mfght greater than its original he+p)ltu7d, mfm( y0jh might? Explain.

Suppose you lift a suitcase fxkt am-id99254g3ulim 0d .on cs0iqcrom the floor to a table. The work you do on the suitcase depends on whicxmn4lm0s5.3 ad2c99 0tcdgk-ioui qih of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed ratg.aq *4tzb+ij/ o+jbx 9m.big her than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb sn mx(4+b xfnu5traight up?nxmu(nxbf 54+

Recall from Chapter 4, Exampfj.3 :vae fa 43cvx*m*xcioj/le 4–14, that 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? Account for this, using energy cov: 3jxx4 o/vf3m*.ajfie cca*ncepts.

  How much work is done by the um4+;en 5fb icgravitational force when a 265-kg pile driver falls 2.80 ;ecn f5+4i bumm?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work is ro01m -+fwrw: 2nbb uppequireb-p nrb1+w:u0w2 pofm d?    J

  A 1300-N crate rests on the floor. How much work is reqj 6ao(ox3bt (vuired to move it at constant speed (a)j6 ov(3a txo(b 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 mojs3628*dk tse6uyn rm vers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficimr*nk sjdys8 6u2t36 eent of friction was 0.50?    J

  A box of mass 5.0 kg is accelv5c4)x zrg hm2erated by a force across a floor at a rate of for 7.0 s. Find the net work do vch r52xm)gz4ne on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat o0ne2 f5hnoa:xo-t,q b n a table. How much work is rea-t 05o,f2q oebhn:x nquired to stack them one on top of another?    J

A lever such as that shown in Fig. :s9 u xkbd*uhbnm:ve pn5- y)66-35 can be used to liff objects we might not otherwise be able to liff. Show that the rauxv n-*hbd:s :6kb 95nmeupy )tio 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 dcxb5ykd:klu y2w3 nr+w7 ww ,.own a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to w ukwdkw7b ,y 3:n+r25yx.lw cthe incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopte6q3/ -k.r+ka m v/if(fx4ze joiqdn r:r of mass M an acceleration of 0.10 g upwai4.o+( k/ q:r6njkm/dqr3vf fizx-eard.    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 distitt c4i ap14w7 lrk*q9,k ef(naj1z )hance axis 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, actin bityj f*84b-pg along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from jb-f4*btp8yix=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 particl4e3lze*,wdc ke 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, ,e4u(rm ai- cu( p6;qjlax ot9an oxygen 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 speed increaslku7 ,b o,.pfned? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an elc39 g.nxh)z zy2)bjgoectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 done4n27z 5;vffav rk,bpc6*fbm tebjy 27 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 n1wjgstbc c ;gf)g8/5 110 N on the arrow over a dista jt5ng/wcs g ;f)g8c1bnce of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s movesd8hvw)-;0qvfi -kg jrf i.x3s a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the hxi ;0.8 v3-d)wsqvfig fkjr-ball on the glove?    N

If the speed of a car is increased by 50%, by what fl3 6hyebn5zb5xk2 f4aactor will its minimum braking distance be increased, assuming5efk5h2nb6z34yb lx a all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investiga z.h /c3dfvoq w/+2qhitors measure a car’s skid mark to be 88 m long. The acci3z .+qih f/wch2do /vqdent 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 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 pitchehl/rac31amr1 d at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the avm1ac r3lh1 /arerage 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-ewv kqsz6s5/ pv.,gd qkb6p 2 go if thrown straight up by someone who does 80.0 J of work on ikvge v qp,zbsk/pd 2qw6s5.6 -t? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration mp-; k/ph eaf/f+n5 /ud(unjjby a single cable. Determ kfudf;j5 n(//panj+u mep/ -hine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much must this spriwib qf jq r0:34*m;mikng be str0fi; q:mrb *4kmijw q3etched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is 5v8a g/(d5feh ,gcso tthe change in potenti sfeg/8 ao,gc v55th(dal energy?    J

  By how much does the gravitational p w*j6n-)o -d 2ji3hidapw oi9dez7 4szotential energy of a 64-kg pole vaulter chan4)w3-n-jispze2ah oz76 d*ji 9 owdi dge if his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speep16g rs/bn;fz0k j urohf53d2d 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 the pfgfuj53k 261; h/ ndos0bz rrspring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 mck0 mnq 7ljk3j xeh.rsg;- s:( above the ground. What is the potential energy of the book rejs-ec.: x js37m( hr0qgk ln;klative 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 anb1dam kb 5i7ror5hug9g ,g c*;d climbs to the top of a 3300-m pea5ck*7 mbggiub ;g, 1dhrra5o9k.
(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 ve2l bf4v:. ;uv- vcsvtertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring li. lu ;e2f:v 4-vcvsbtvne up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top3; lb1 d cjcu0l(;q srbj5 j;kpuo9z8t speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upward?;b sd 3qjtlj9cbcpzkl(r580o; 1;uu j    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from re abn9mhb: o tjz65ofi90x,3nt st, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frt qtr +mi;5v+;cwrz(gg;jtf 2.q itf8ictionless 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 gravi-a47zc )qb cebtational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her cente-bc7qbc4)ea z r of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps verticall7x )//qin5 lx 80jrciu5zkde ly upward from the top of a platform with al leiqdx/ ij cn0)58k/u7 z5rx speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness constant is 950y )pg9y9 f oa(cc+3vrmrfo9b -N/m is attached to a a f)9 ( 3gy-pvb c9yr+rf9mocotable and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slidrlkmd hl:5z* (es without friction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whd k:(rml5z lh*ose 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 stiffntjkh.x a: 1b)*3 o.bkx(qc jfh( tt-nsess constant k), Fig. 6–40. The block is given an initial displacembt kqb1 f*xkjh.nta c-o)h( j( 3x:.tsent $x_0$ 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. Sheuhf*:n8hps 3b m*zd8kgk /1x mp-i1qx 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*ghdz/xp nmf:*8bkxm3p1q h18s-i ku k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 whe54bjc xt iri4t5i.p2 jre it is released from5rij4itpx4 t5 2.cjib 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 an angle of 33 n-0 yqziii do-q fc8cdg,q16ref r;;*$^{\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 brxds99x g4o7:d e8jvy e 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 r4:9xxvdgd9 so8ey 7 jconstant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a2 tq)bz xbc/t, 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 oem+;mt.4:sj v.tj a-u09yckydl r qd /mkwf;,f mass 7650 kg and traveling 95km/h in opposite directions, collide he;q:.wcm .yj+arkled4mk/ uj dsf 0;, tm v-9ytad-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reachessucr88 uixmz; 3 3kxb9 the bottom with a speed of 2.2m/s How much thermal energy due to friction was generx3u ;zkrcm xbi93u 88sated in this process?    J

  A ski starts from rest and slides down 7ly9 wal hb ho)w4(6ypx,f(mn 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 13.0 m above h/,7rkft9 b4my(alffg)6 on v 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 heighfv 78dr0zo h;vnz1p j,t of 2.0 m, and it bounces back to a height of 1.5 m.zz78dh;npv1, r vf0 oj
(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 across a*xd+cu9,qimdgan)q (*n 6n x zwm2w-x floor with a constant horizontal force of 350 N. For the first 15 m the floor is * *nx )uxd i+qw69 z cnmdw(axq2ngm,-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 coaster in Fig. 6–41 passes point 1 with a speed of If thege)9iwsb b5)de4 a,t n average an4b eg,95)e t)wsidbforce of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches pkrih g 81a02l1*l3g eni-fi-rp l ew3the foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light v3lx4 5cjhti/ horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted /i l3vt c4j5xhthat the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light aji;f cjiqe3kip8s2( ,ct qn7, vb3l( 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 compresbvfk 8p32 (n c7,i3q(,stc;aji qejlises the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of rcsjia4/s* ,qj* a m2r980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventualqsrsr,j 2mc/**a4 ji aly landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to liftbqmjz.h+iid oi*9e es g,).w8z*zc+s a 315-kg piano to a sixth-story window 16.0 mimdhgzi ,9* z ).cso*.wzesb+qeij +8 above?    s

  If a car generates 18 hp when traveling awfre8r6k3 ve0t a steady 88km/h what must be the average force exerted on the car due to friction andkwr f3 8r06vee air resistance?    N

  A 1400-kg sports car accelerates from rest to 9:wx 8on :lcw7t5km/h in 7.4 s. What is the average power delivered byx: c8lwto7wn : the engine?$\approx$    hp

  (a) Show that one British hors,vl c2xsopw53 epower$ \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 ini iag(r- t1m20srhba/ 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 5tpc0jwkm : x2car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately whatpkc02txm :j5 w power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a (-i/vcq9beoq3j lhj. l+ +rke3.0-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to hbmn fl du,)9m -hnzd 9ul;d*314m/s If this motion takes 1.5 s, 9*u;n- bz)ln93lfdmhd, humdwhat average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water 4)mykkuj3yo x;1 kxkdv o afk,-tho*m+ )z,9mper minute through a height of 3.60 m. What output ratingfyx*x 9vmmk,dm- kta)u13okkhz+ ,k ;j4o)oy (watts) should the pump motor have?    W

  During a workout, the football player(n( li8ujfafl cb2(m. s at State U. ran up the stadium stairs in 66 (( ill2(nm c.ffu8 bjas. The stairs 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 clispq ..-nq x8kgw;x xmn uu(b74mb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power outpuvjfjz0+ gyv g)k5zeb6v.3 o0vt of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces add up t+ 5vzb3zvgojvfk) v y. 6jeg00o 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg box along ; gfdg80ly zw/a l ;y/0 zfgd8gwlevel floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.08c h3k9l lmg(aozdb bi/ 8r4v7 $^{\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/hwwol (*:9cdj q) 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 (:*j o w9qlcwdbe, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 o2w. zodm mc7 11-ekaxcm 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 books ar2z .d71m k-o1cxemo wae all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) i/ am lfso+e;b(n the 1936 Olympics shows that his center of mass rose 1.1 b (/a+oem;fsl m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shov* tnyzt kzu6jc:8j1 8wn in Fig. 6–39 is to remain on thezyv k*16tj 8 8t:ujnzc 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 37i*2t/yb e*aff 0 m after jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, bt byia*2f f/*eut survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other 3n0ywsll)mpyp1n7 x .a fat(1 end is fixed (Fig. 6tsn.70(3yp1wnfpm xal)ly 1 a –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 mountaibyn;c:pv zu:o*m8 ha5pqd/:rn. The climb is made in 5.0 h starting at an elevaamp*c ;br/5hu8nz:vpq d::yo tion 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 elevator is 28 m above a huge s1iwi5/a cws+om6bbs*s i46hfpring ($k=2.2\times10^{5} \mathrm{N/m}$) 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 movr*cgh/m:bi2iht ,-ip /cw d-ce 47,000 people per hour. If the average lifiihwbcpd /-g,crct-mh:/* i 2 t 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/sm cb*1id d-gs9/g heunem(*4 k and falls vertically 81 m before striking the turbine blad9de*s kh(41nmi dmeubgc/g *- es. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a rollerywz1hj0;vy4 g z:+ duk coaster with a circular vertical loop (Fig. 6–44), the difference in your appareyv;j1+ y:hzkwd04g zunt 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, 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 directl1olx*idah7 cnr g0 a0+m867 fu;8ivmumdqi p0y into work, how high could an 82-kg man climb a ladder if he were fueled b7i60 m xidvu0dr8+ f7umca ap;g lo*mn80i1qh y 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 upwardx+(6q prf rpg( 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 inside the scale co:lusro8gei-i 7-,w6p2 g mov ;0vvypo mpresses 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-pgvmgi,iolv0pow;v o27 8ys 6-eur: at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a b f m7r,ohc4 gbu47/ ltvv()4pzuu*xk lake (Fig. 6–45). He releases the rope wheglhcv)o u4fbb*/7 7zv uur4(txp mk,4 n 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 s)idh)*rr 4z gin 9.0 s. W rhzds) 4g*ri)hat minimum power output was used to accomplish this feat?    W

  Some electric-power compani2scs m -p39eo twwm+zb)9 st:2mcb9kbes 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 1.0 hour by a 120-MWkmwb bw)+z c:tsc-9 2 ss9m3t bme9p2o ($120\times10^{6}$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 cuen)5wfqj e) v0t in half. What is the spring stif0 5fje)nevq w)fness constant for each of the two resulting springs?   k

  A 6.0-kg block is pu2,y;misgg i3t b zkc0y2v pp2:shed 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 ci q/l6oq *b*t35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, andq/obqcl*t 6i* neglect frictional losses.    s

  In a common test for cardiac function (the e5 y75mkkm5dwmo -gw+“stress test”), the patient walks on an inclined treaddgw-5m k 7owey +mm5k5mill (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-t a1cj )/q ex(mvf/yy8kg rock vertically upward a distance of 500 m, what was (fyv 1axe t/j)8c yq/mits 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 height of un 94mvbq6yi 5/fe5 he2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum power o4i/ h5venbmue95q 6f yutput?    W
(b) What is the speed of the water as it hits the wheel?    m/s