Solving the Balanced Board Problem

[splac6996]

Homework Statement

Two people are standing on a very light board that is balanced on a fulcrum. The lighter person suddenly jumps straight up at . Just after he jumps, how fast will the heavier person be moving?

Homework Equations

M1*(Vf1) + M2*(Vf2) = M1(Vi1) + M2(Vi2)

The Attempt at a Solution

I tried using this equation but I did not get a likely solution I think I should include the distance that the two man are apart but I do not know what to do with that.

 

[learningphysics]

I believe you need to use conservation of angular momentum about the pivot of the fulcrum... the torque about the pivot is 0... hence the angular momentum isn't changing... we can't use conservation of linear momentum because of the external forces like gravity and the force exerted at the pivot of the fulcrum.

 

[splac6996]

so i know the mass of both men and the tangential velocity for one of them so from that point do I set the following equation equal to one another to solve for tangential velocity of the second man.

L(angular momentum)=m*r*v(tangential velocity)

 

[splac6996]

Thanks i figured it out using that equation but r should be r^2 for both sides.