# Change in potential and kinetic energy

1. Apr 23, 2009

### science_rules

1. The problem statement, all variables and given/known data
how is the change in potential energy related to the change in kinetic energy?

2. Relevant equations
i just know that for a tossed object, the KE decreases, and its PE increases until it reaches the top. Then it has potential energy at the top, and its KE increases, while its PE decreases. im not sure how to relate the change in PE and KE though.

3. The attempt at a solution

2. Apr 23, 2009

### Hootenanny

Staff Emeritus
It very much depends whether there are any non-conservative forces acting on the system. If there are no dissipative forces acting on the system then the sum of the kinetic and potential energies is constant.

3. Apr 23, 2009

### rl.bhat

Tha rate of change of potential eenrgy = dp/dt = mg*dh/dt = mgv
Rate of change of kinetic energy = dE/dt = 1/2*m*2v*dv/dt = mgv.
So they are equal.

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