A ball of mass m falls from height h, to height h f near the surface of the Eart

Question

A ball of mass m falls from height h,to height hf near the surface of the Earth, as shown at right. When the ball passes it has a speed vf. Ignore air resistance, and assume that any changes in kinetic energy of the Earth are negligible.

In this problem, you will analyze this situation by considering two different systems: system BE (the ball and the Earth) and system B (the ball alone).

b.Consider the system of the ball only, system B.

i.As the ball falls from h{ to hf, does the total energy of system B increase, decrease, or stay the same? Explain by considering the net external work on system B.

ii.Write an expression for each of the following quantities in terms of the given variables and any physical constants.

Explanation / Answer

KE = 1/2 m*v^2
PE = -m*g*h
So the change in kinetic energy of the system is 1/2 m v^2
the change in potential energy is -m*g*h
The net external work is zero, because all the changes are internal
So I would say 1/2 m*v^2 -m*g*h = 0 which is the total net external work.

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