# Homework Help: Circular Motion of a moving rock Problem

1. Oct 16, 2014

### KrazySocoKid

1. The problem statement, all variables and given/known data
You hold a bucket in one hand. In the bucket is a 480g rock. You swing the bucket so the rock moves in a vertical circle 2.8m in diameter. What is the minimum speed the rock must have at the top of the circle if it is to always stay in contact with the bottom of the bucket?

2. Relevant equations
N + mg = mv^2/r

3. The attempt at a solution
I thought this was going to be a simple answer. So I set N = 0, because that is the when the rock is about to lose contact. So then I solved for v = sqrt(r*g), which is sqrt(9.8*2.8) which gave me 5.2 m/s, but it is saying it is wrong? I think my problem must be than N must be something other than 0? But I'm not sure what to put N as in that case. Can someone help me?

2. Oct 16, 2014

### PhanthomJay

N is 0 for sure, but you used the diameter instead of the radius!

3. Oct 16, 2014

### KrazySocoKid

Well, damn. Thanks mate haha.