# Work out the velocity from the momentum?

1. Oct 19, 2007

### ryansmith885

1. The problem statement, all variables and given/known data
Does anyone know if it is possible to work out the velocity from the momentum?
206Kg ms^-1 is the momentum... thanks
ryan

2. Relevant equations

3. The attempt at a solution

2. Oct 19, 2007

### learningphysics

do you have the mass?

3. Oct 19, 2007

### ryansmith885

no i dont have the mass just the mometum

4. Oct 19, 2007

### learningphysics

Then it's impossible to get the velocity... the velocity could be anything...

momentum = mv
v = momentum/m

plug in difference m's and you get different v's...

5. Oct 19, 2007

### ryansmith885

thanks for the formula.... if two skaters collide 1 has 75kg mass (180kg ms^-1 momentum) and the other has 60kg mass (100 kg ms^-1 momentum) than the total size of momentum before the collision would be 206 kg ms^-1 right? I want to calculate the velocity of 206kg ms^-1 thanks

6. Oct 19, 2007

### ryansmith885

7. Oct 19, 2007

### learningphysics

How do you get 206?

you need to consider direction also... if they collide I assume they're going in opposite directions?

Then if the momentum of the first is 180, and the other is 100 in the opposite direction... I'll call it -100 taking the direction of the 1st skater as positive...

so total momentum = 180 + (-100) = 80kg*m/s

So total momentum after the collision is also 80kgm/s by conservation of momentum.

Now once they collide are they sticking together? Then using the definition of momentum and a total mass of 75kg+60kg... you can solve for the velocity using the momentum of 80kgm/s.