What Is the Speed of a Block at Different Points on a Frictionless Hill?

[misyg]

A 250g block slides down a frictionless hill. If the hill is 1.2m high and the speed of the block is 5 m/s when it is halfway down, what was the speed of the block at the bottom and at the top?

I tried using the equation KE(top)+GPE(top)+SPE(top)=KE(middle)+GPE(middle)+SPE(middle) and the same for the middle+bottom But I just could not figure out the correct answer.

 

[MacDougal87]

Assuming your SPE is spring potential energy, and you're setting that value to zero, you're on the right track. Can you post your actual calculation steps? I should be able to point you in the right direction if you show me how you plugged your numbers in for your calculations =)

 

[misyg]

I set them equal to zero, the SPE, and came up with the equation for the top and middle of the hill...top(1/2mv2)+(mgh)=(1/2mv2)+(mgh)middle...(1.25v2)+(2.94)=(3.125)+(1.47)
v2=1.324
vtop=1.1507

does that sound correct.

 

[MacDougal87]

Well, the approach was fine, however it looks like you made a little mistake on converting your mass, judging by your coefficient in front of v². it looks like you used the correct mass for the rest of your values however, so it must have been just a little slip up for that one. Try solving it using .125 instead and see if that gets you your answer =)