Circular motion , the loop the loop

[NihalRi]

Homework Statement

The loop-the-loop machine has radius R of 18m
(a) What is the minimum speed at which a cart must travel so that it will safety loop the loop
(b) what will the speed at the top be in this case

Homework Equations

Centipetal force = m*v^2/r
Kinetic and potential energies = (1/2) m*v^2 and mgh respectively

The Attempt at a Solution

(a) equating weight and centripetal force and then solving for v I got an answer for velocity of 13.2 but the actual answer is 30
(b) based on (a) calculate the velocity using energy equations
(1/2)m×v^2 = mgh + (1/2) m×v^2

 

[Doc Al]

(a) equating weight and centripetal force and then solving for v I got an answer for velocity of 13.2 but the actual answer is 30

I believe (a) is asking for the speed at the bottom. (Solve (b) first.)

 

[NihalRi]

I believe (a) is asking for the speed at the bottom. (Solve (b) first.)

I get what it's asking just not how to get the answer

 

[Doc Al]

You solved part (b).