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219_Physics ProblemsTechnical Physics

# 219_Physics ProblemsTechnical Physics - Chapter 8*P8.8 The...

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Chapter 8 221 *P8.8 The energy of the car is Em v m g y =+ 1 2 2 v m g d 1 2 2 sin θ where d is the distance it has moved along the track. P == + dE dt mv dv dt mgv sin (a) When speed is constant, ° = × mgv sin . sin . 950 2 20 30 1 02 10 4 kg 9.80 m s m s W 2 ej bg (b) dv dt a = 22 0 12 0183 . . ms s 2 Maximum power is injected just before maximum speed is attained: = × mva mgv sin . . . 950 2 2 0 183 1 02 10 4 kg m s m s W= 1.06 10 W 24 (c) At the top end, 1 2 950 2 20 9 80 1 250 30 5 82 10 2 2 6 mv mgd += + ° F H G I K J sin . . sin . kg 1 2 m J 2 *P8.9 (a) Energy of the object-Earth system is conserved as the object moves between the release point and the lowest point. We choose to measure heights from y = 0 at the top end of the string. KU g i g f + : 0 1 2 2 + mgy mv mgy if f 98 2 30 1 2 2 298 2 1 229 2 .c o s . o s . m m m 2 af a f −° = + =− ° = v v f f (b) Choose the initial point at 30 and the final point at 15 : 03 0 1 2 15 2 1 53 02 9 8 2 1
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