# Mechanical energy

1. Oct 28, 2009

### stefisc

A 48.0 kg block slides along the frictionless surface of a hill that is 188 m high with an initial speed 19.0 m/s. Relative to the bottom of the hill, (Note that the acceleration is not constant so you can not use freefall equations to solve the following problems.)

What is the block's mechanical energy when the block is 75.0 m above the bottom of the hill?

What is the block's speed when the block is 75.0 m above the bottom of the hill?

2. Oct 28, 2009

### Bloodthunder

you should be able to use conservation of energy seeing that the slope is frictionless, and all you need to know are the horizontal and vertical initial speeds.

3. Oct 28, 2009

### stefisc

i know the equations:

ME=KE+PE
KE= 1/2 mv^2
PE= mgh

my problem is that i don't know how to use them and i need someone to explain it to me.

4. Oct 28, 2009

### ApexOfDE

You have total energy of block is: E = K + U. Base on conservation of energy, you have E0 = E1 <==> K0 + U0 = K1 + U1. You already have initial velocity ==> K0, height of hill = 188m ==> U0, height of hill at time t 75m ==> U1. Plug them to CE equation, you will find K1.

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