1 to 2 Interactions, or explosions

[lucky47]

1 to 2 Interactions, or "explosions"

I'm stuck doing this problem on my physics homework.. it's different than the type of problems we have been doing in class, and he hasn't taught us the equation to solve this question. The problem is: Tim, mass 50.00 kg, is riding a skateboard, mass 2.00 kg, traveling at 1.70 m/s. Tim jumps off and the skateboard stops dead in its tracks. With what velocity did he jump?

Can anyone tell me what equation to use in order to get the answer?

 

[BerryBoy]

Think of momentum...

The skateboard has a cerain momentum of 'mv'. What velocity would Tim have to jump off of the skateboard to cause the final velocity of the board to be zero?

Use conservation of momentum before and after the jump (remember Tim has initial momentum).

This is neglecting the vertical component of Tim's jump.

Regards,
Sam

 

[lucky47]

Hm.. I'm not quite getting it. So to figure out the momentum of Tim, it is 50kg, his weight; times the velocity of the skateboard, 1.7m/s, correct?
And now the momentum of the skateboard is 2kg times 1.7m/s..
Now to find the velocity i take the two numbers I got from solving the above and divide it by the mass of the skateboard?

Am I remotely correct in what I am doing?

 

[BerryBoy]

Firstly, let's clear something up... Momentum is the product of velocity and MASS (not weight: weight is a force).

You have worked out the total momentum before the jump, but note that the velocity of the skateboard is now zero, so dividing by its mass is not useful.

Tim after the jump however, has a momentum mv (you know his mass), what is v?

Sam.