physics
posted by Linn .
I have a diagram of a roller coaster. It starts at a height of 100m where the v=0, it then drops completely to the ground and then goes into a loop that is 75m high; the point where the loop starts is point A. From the loop, the track raises to e height of 50m (this is point B) and then the track goes up to 80m, there, another loop forms (this is point C) and then the track goes up again to now a height of 90m at point D.
Find the velocity of the roller coaster at each point.
I'm not sure how to do this because I don't have the mass to do GPE=mgh. Please help.

You don't need the mass. Write the conservation of energy equations and you will see than the mass m cancesl out.

I tried doing that; can you please explain.
Wait, so, would the first velocity be mgh=1/2mv^2 and then I take away the m's? 
Also, I think I've found the first velocity, but would I disregard that when finding the velocity at point B?

yes.
The sum of V^2/2 (KE/m) and gh (GPE/m) is a constant everywhere.
(This method neglects friction and the rotational kinetic energy of the wheels, two assumptions they probably expect you to make.) 
oh okay, thank you very much. :)