Welcome to PHY 121 Blog Help. Here's how it works. For each homework question and lab report we will make a post, this will probably contain a few tips on what the problems are about and how to solve them. If you are stuck on something then instead of emailing us directly you should post a comment in reply to the relevant post. We will try to guide you through tough points and help you understand the problems and the concepts behind them.
The problem doesn't tell us it is elastic, so we have to decide ourselves. We can do this only after getting the speeds before and after the collisions and doing the energy conservation calculation.
Momentum is conserved because there are no external forces. So you vsn use momentum conservation to get the unknown speed, and then check is kinetic energy is conserved.
By "change in KE equation" do you mean the difference between the total KE after the collision and the total KE before the collision? This is the correct thing to do.
8 comments:
See equation 7.3 in the lecture notes
I thought elastic collisions had no change in kinetic energy but the answer isn't 0.
The problem doesn't tell us it is elastic, so we have to decide ourselves. We can do this only after getting the speeds before and after the collisions and doing the energy conservation calculation.
Momentum is conserved because there are no external forces. So you vsn use momentum conservation to get the unknown speed, and then check is kinetic energy is conserved.
And I would also add to remember your signs when submitting your answer!
i am using the change in KE equation and I am not getting the right answer. what am i doing wrong?
Try using more sig figs in your answer, that solved the problem for me.
Final KE-Inital KE= DeltaKE
By "change in KE equation" do you mean the difference between the total KE after the collision and the total KE before the collision? This is the correct thing to do.
Post a Comment