Circular momentum - Loop-the-loop question.

[Ripe]

Homework Statement

A loop-the-loop machine has radius 18m. What is the minimum speed at which a cart must travel so that it will safely loop the loop?

Homework Equations

centripetal acceleration: v^2/r
velocity=(2r*pi)/t
Perhaps more?

The Attempt at a Solution

To be honest, my main problem is that I'm not really sure where to start. I calculated the displacement a cart must travel, i.e. the circumference of the diameter, but I don't know what to do next..

 

[LawrenceC]

You want gravity to be nullified by centripetal acceleration when car is at highest point.

 

[Ripe]

Ah. You mean that when it is at the highest point, the centriputal acceleration will have the same magnitude and direction as gravity and thus, we can deduce that the centriputal acceleration is 9.8ms^-2?

 

[LawrenceC]

That's it.