Homework Help: A collision, help me double check this ?

1. Apr 6, 2013

Jbreezy

1. The problem statement, all variables and given/known data
A mass, m1 = 4.5 kg is released form rest 2.5 m above the ground on a inclined plane (35 degrees). m1 slides down incline and makes a smooth transition to flat plane then strikes m2 = 8.2 kg, which is at rest, calculate the speed of both masses after elastic collision and find how high m1 will go back up the incline.

2. Relevant equations

3. The attempt at a solution

Part 1.
Figure out how fast m1 is going after traveling down incline.
So,
mgh = 1/2 mv^2
manipulate for v and you get v = sqrt(2gh)
sub in values and you get v = 7m/s
Part 2 the collision
We will use
Vi2 = (m1- m2/ m1+m2) (vi1) + 2m2/m1+m2(v2I)
The V2i is 0 so it is gone.
Vi2 = (m1- m2/ m1+m2) (vi1)
We substitute in the values and we get -2.03m/s
For mass 2 we use.

V2II = (2m1)/ (m1+m2) (vi1) + (m1-m2/ m1+m2 )(V2i)
V2i once again drops out
V2II = (2m1)/ (m1+m2) (vi1)
Sub in values and we get 4.96m/s

Lastly get the height for mass one back up incline.
We know the velocity so we can use
1/2mvII = mgh
solve for h and get h = VII/2g
And I got .104m

I hope it is right please double check me.
Thanks

2. Apr 6, 2013