Part A Standing on ledge about 1 meter off the ground, you step off knowing you

Question

Part A

Standing on ledge about 1 meter off the ground, you step off knowing you can manage the impact. When you first start to fall downward, you have no initial velocity and your momentum is zero. However when you reach the ground you will be moving at gt m/s, where g is the acceleration of gravity and t is the time it takes to get to the ground, in this case roughly 4.4 m/s after 0.45 second.

From the standpoint of an observer on the ground watching, you have momentum 4.4 times your mass in kg-m/s. From the standpoint of someone watching from afar and seeing both Earth and you, what is the total momemtum of you and the Earth together?

a. Twice your final momentum.

b. Zero. There is no outside force, so momentum is conserved. It starts and ends at zero.

c. Zero at the beginning and ending with your final momentum but upward, as you would perceive while falling.

d. Zero at the beginning and ending with your final momentum downward, the same as perceived by an observer on the Earth watching you.

Part B:

Raise a mass 19.6 kg to height 3.9 in meters, then let it go. How much kinetic energy does it have in joules when it reaches the ground?

Assume the acceleration of gravity is 9.8 m/s2.

Explanation / Answer

Conservation of momentum is a fundamental law of physics which states that the momentum of a system is constant if there are no external forces acting on the system !!
b. Zero. There is no outside force, so momentum is conserved. It starts and ends at zero.

(B)
Using Energy conservation,
Intial Potential Energy = Final Kinetic Energy
Final Kinetic Energy = m*g*h
Final Kinetic Energy = 19.6 * 9.8 * 2.9
Final Kinetic Energy = 557 J

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