# Homework Help: Uniform Circular Motion

1. Oct 23, 2013

### QCHabsQC

1. The problem statement, all variables and given/known data

A ball of mass 4 kg on a string of length 1.5 m is being swung in a circle in the vertical plane at a constant speed of 10 m/s. Find the tension in the string at the bottom and top of the balls path

2. Relevant equations

ƩF = m(v^2/r)

3. The attempt at a solution
This is how I attempted to solve this problem, but my answer is not correct.
Is it correct that the tension in the string at the bottom is: T = m(v^2/r) + mg
And at the top: T = m(v^2/r) - mg

Last edited: Oct 23, 2013
2. Oct 23, 2013

### Simon Bridge

Consider:
T = m(v^2/r) + mg

This is saying that, at the bottom of the path, the tension has to overcome gravity and still have enough left over to give a centripetal force.... the net force points upwards.
Does that make sense?

3. Oct 23, 2013

### QCHabsQC

Yes; so the tension at the bottom would be, T = (4*(10)^2)/1.5 + 9.8*4 = 217 N. Is this correct?

4. Oct 23, 2013

### Simon Bridge

I don't check arithmetic.