What is the correct formula for finding tension in a pendulum bob on a string?

[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?

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.

 

[Doc Al]

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

 

[chxmilan]

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

 

[Doc Al]

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

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

 

[agostino981]

I would suggest you to use energy instead.

 

[Doc Al]

I would suggest you to use energy instead.

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