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KatlynEdwards
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Homework Statement
A ball of mass m falls from height hi to height hf near the surface of the Earth. When the ball passes hf it has speed vf. Ignore air resistance, and assume that any changes in kinetic energy of the Earth are negligible. Also, the starting velocity of the ball is zero.
Write an expression for each of the following quantities in terms of the given variables and any physical constants. If any of these are zero, state so explicitly.
1. The change in the kinetic energy of the system (the ball and the earth).
2. The change in potential energy of the system.
3. The net external work by external forces on the system
4. Now write an equation that relates the expressions above and use it to solve for the final speed of the ball.
Homework Equations
KE = 1/2 m*v^2
PE = -m*g*h
The Attempt at a Solution
1. So the change in kinetic energy of the system is 1/2 m v^2
2. the change in potential energy is -m*g*h
3. The net external work is zero, because all the changes are internal
4. So I would say 1/2 m*v^2 -m*g*h = 0 which is the total net external work.
Solving for v I get the square root of (2*g*h)...
Although I don't recognize this formula.
Can anyone tell me if I'm doing something wrong?
Thanks!