You drop two objects from a cliff (h = 200.0 meters) in an area where the Earth\

Question

You drop two objects from a cliff (h = 200.0 meters) in an area where the Earth's = 125 N/C. A rock of mass 5.0kg. A group of 323 electrons ( mas and charge can be found using the back of your textbook) Before hitting the ground the velocities are: vi= 58.8m/s vii= (0.3128 c) m/s (c = speed of light ) How much initial PE the object has. How much final PE the object has just before hitting the ground. How much final KE the object has just hitting the ground. The total work done by none- conservative forces. If the answer is non-zero, what non-conservative forces do this work?

Explanation / Answer

1. for rock

initial PE = 5 *9.8 *200 = 9800J

initial KE =0

final PE =0

final KE = 0.5 *5 * 58.8^2 = 8643.6

work by nonconservative forces = 9800 - 8643.6 = 1156.4 This work is done by air friction

2. charges

initial PE = Eqh = 125 * 1.6 * 10 ^-19 * 323 * 200 = 1.292 * 10^-12

initial KE =0

final PE =0

final KE = 0.5 * 9.1 * 10^-31 * (0.9384* 10^8)^2 *323 = 1.294 * 10^-12

diffrence of thse two is 0.002*10^12 which is very less because the mass of electrons is very less so the effect of airfriction is negligible

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