How Do You Solve Momentum and Impulse Problems?

[amyiish]

Can anyone help me solve these questions on momentum and impulse? Thank you!

1. A 55 kg swimmer is standing on a stationary 235 kg floating raft. The swimmer then runs off the raft horizontally with a velocity of +5.3 m/s relative to the shore. Find the recoil velocity that the raft would have if there were no friction and resistance due to the water.

2.In a football game, a receiver is standing still, having just caught a pass. Before he can move, a tackler, running at a velocity of +5.0 m/s, grabs him. The tackler holds onto the receiver, and the two move off together with a velocity of +2.6 m/s. The mass of the tackler is 119 kg. Assuming that momentum is conserved, find the mass of the receiver.

 

[radou]

Hello amyiish, and welcome to PF.

In order to get help, you should show us some attempts and share some thoughts on the problem with us. After doing so, we'll be glad to lead you through if you get stuck.

Edit: also, such questions belong to the 'Homework & Coursework section', but don't repost, it will be moved to that section soon enough, I assume.

 

[amyiish]

I figured out how to do the second one, but I still need help on the first one. I'm not sure what equation(s) I'm supposed to use. Pretty much clueless, actually..

 

[radou]

I figured out how to do the second one, but I still need help on the first one. I'm not sure what equation(s) I'm supposed to use. Pretty much clueless, actually..

It's a conservation of momentum problem, too. Still clueless?

 

[amyiish]

Should I use: mv1 + mv2 = m(1+2)v(1+2) ?

 

[amyiish]

Oh, I got it! I just forgot it would be negative. Thank you. :)

 

[radou]

Should I use: mv1 + mv2 = m(1+2)v(1+2) ?

Simply use conservation of momentum. The velocity of both the man and the log equals zero first, which sets one side of your equation equal to zero.