# Homework Help: Maximum velocity at the lowest point

1. Sep 26, 2011

### helpinghand

Say that there is a car on a top of the hill and it was on a frictionless surface, explain why the maximum speed of the car would occur at the lowest point of the hill?

In this case would you prove it through the conservstion of energy PE + KE = PE + KE?

If so, how does this prove that Vmax occurs at the lowest point?

Any help would be great, Thanks :)

2. Sep 26, 2011

### daveb

What can you say about PE at the top vs at the bottom? Which is higher?

3. Sep 27, 2011

### helpinghand

Assume that there is no PE at the top of the hill...

What do you mean which is higher?

4. Sep 27, 2011

### viplav

PE is a relative phenomenon. U cant say that there is no PE at the top.
if there is no PE at the top......PE at the bottom should be negative

5. Sep 27, 2011

### helpinghand

Oops... typo, PE = mgh and KE = 0

6. Sep 27, 2011

### viplav

hi friend

Assume that height of the hill is 'h' m.

now initially as the car is rest on the top of the hill.......KE is zero and PE is 'mgh'

when the car is at the bottom of the hill the total PE at the top should be KE at the bottom........since PE at the bottom is zero

At any point in between top and bottom....the total energy is the sum of both PE and KE.....but at the bottom the total energy is only KE so v is max at this point