Need help with Momentum and Collisions

[mike305]

Need help solving this problem
http://img409.imageshack.us/img409/5854/chp851yx1.jpg

Thank you

 

[cristo]

Hi, and welcome to PF. Please give your thoughts on the question, before we can help. Better still, use the posting template with which you were provided!

 

[turdferguson]

What is the momentum before the block is released? How about after? Then you can use energy for the second part

 

[mike305]

the momentum before the release is 0, and after is 2. I understand that i need to apply conservation of momentum in this problem somehow, but I don't see a way so far.

 

[cristo]

the momentum before the release is 0, and after is 2. I understand that i need to apply conservation of momentum in this problem somehow, but I don't see a way so far.

Conservation of mmtm states that mmtm before=mmtm after. Think of the total system. Before the block starts moving, like you said, p_i=0. When the block hits the horizontal surface, the total momentum p_f= 0.5*4-v₂*m₂. (The negative sign appears, since the block moves to the left.) From this you can find the velocity of the wedge.

Can you carry on from here?

 

[mike305]

v2 = 2/3 m/s ( to the left) ?

and for part b, should I use convservation of energy (potential and kinetic) in order to find the height?

 

[cristo]

v2 = 2/3 m/s ( to the left) ?

and for part b, should I use convservation of energy (potential and kinetic) in order to find the height?

I've not checked you calculation, but yes, it's to the left.

For b, as you say, you should use conservation of energy.

 

[mike305]

thank you very much for your help

 

[cristo]

thank you very much for your help

You're very welcome!