# Homework Help: Pendulum bob on a string

1. Feb 7, 2012

### chxmilan

A 2 kg pendulum bob on a string that is 3m long is released with a velocity of 1 m/s when the support string makes an angle of 30 degrees with the vertical. What is the tension at the highest point of its motion?

3. The attempt at a solution
Ok so using Newton's second Law, the equation should be Force of tension =mg cos θ. Adding the numbers in =2 kg (9.80 m/s)cos 30°=16.97 N. However its telling me its wrong and the answer should be 16.6 N. I'm confused as to where I've gone wrong. I realize that I skipped over length of the string but I was told that because we're dealing the the vertical component, its not needed.

2. Feb 7, 2012

### Staff: Mentor

What angle does it make when it's at its highest point?

3. Feb 8, 2012

### chxmilan

Wouldn't the angle still be 30° at the highest point?

4. Feb 8, 2012

### Staff: Mentor

It would be if it were released from rest at that point, but it was given a push.

5. May 4, 2012

### agostino981

I would suggest you to use energy instead.

6. May 5, 2012

### Staff: Mentor

One would use energy conservation to find the highest point, if that's what you mean.