# Momentum and Energy i think?

1. Sep 10, 2011

### Xinyee

Momentum and Energy i think??

1. The problem statement, all variables and given/known data
Block 1 of mass m1 slides from rest along a frictionless ramp from height h = 3.10 m and then collides with stationary block 2, which has mass m2 = 5.00m1. After the collision, block 2 slides into a region where the coefficient of kinetic friction μk is 0.550 and comes to a stop in distance d within that region.What is the value of distance d if the collision is (a) elastic and (b) completely inelastic?

2. Relevant equations
I know M1U1+M2U2=M1V1+M2V2 when it is elastic.

3. The attempt at a solution
So using that equation, i found V2=3.5m/s. But then i have no idea how to find the distance... Help anyone??

2. Sep 10, 2011

### cepheid

Staff Emeritus
Re: Momentum and Energy i think??

No, this is the equation for momentum conservation, which is always true regardless of whether the collision is elastic or inelastic. Be careful as well: the U's and V's are vectors here (velocities) because we're talking about momentum. Since this is a 1D problem, this means they must at least have + or - signs indicating their directions.

The collision being elastic or inelastic determines whether kinetic energy is conserved.

You have to figure out how fast the block is moving when it enters the area where there is friction. Based on that starting velocity, you can figure out how far the block will travel before the friction force slows it to a stop.