Saturday, October 29, 2011

UT HW7: #15

I got 14, and I thought this was an energy problem, so I did mgh=1/2mv^2, but it didn't work. What should I be doing?

2 comments:

Dr. Winters said...

That's right. Initial energy = final energy.

For the initial energy nothing is moving (so no kinetic energy). The wedge is sitting on the "frictionless horizontal surface" so its height is 0 and it has no potential energy. The small block is at a height of h and has potential energy mgh. That's your mgh on the left side of your equation.

For the final energy both the wedge and the small block are on the surface, so they both have h=0 and neither has any potential energy (mgh=0). However, they are both moving so they both have kinetic energy. Did you include the kinetic energy for both the small block moving to the right and for the large wedge moving to the left?
Good luck.

Vicky Timmel said...

Got it, thanks!