# Homework Help: Calculating energy lost in collisions?

1. Oct 25, 2007

### pebbles

My notes don't provide an equation.

I am given inital and final velocity
Vi=50 m/s
Vf=25 m/s

Thanks.

2. Oct 25, 2007

### dynamicsolo

I'm afraid it's worse than that: if you're trying to do an energy calculation, you're going to need a mass as well... If this is a collision problem, you're going to need both masses and the initial and final velocities for each of them.

Are you covering linear momentum in your course right now?

3. Oct 25, 2007

### pebbles

oops forgot to note the masses: each is is 1 kg.

sorry!

4. Oct 25, 2007

### dynamicsolo

Is what you posted originally the initial and final speed of both masses? There still seems to be detail missing from this problem.

In any case, you'll need the formula for kinetic energy. Find the sum of the kinetic energies of the two masses before the collision and compare it to the sum of their kinetic energies afterwards.

5. Oct 25, 2007

### pebbles

agh. no!
what was i thinking?!
ok mass 1= 1.0 kg; initial velocity = 50; final velocity =25
mass 1.0 kg; initial velocity= 0; final velocity = 25

6. Oct 25, 2007

### dynamicsolo

It looks like you now have all the data assembled. How you do calculate the kinetic energy of an object? Find the initial and final kinetic energy for each mass and the total initial and final kinetic energies of the pair.