# Vertical Circle (Circular Motion)

## Homework Statement

You swing a 1.60m long string with a metal ball attached to its end in a vertical circle, such that the speed of the ball does not change but the rope is always taut. The tension in the string when the ball is at the bottom of the circle is 60.0N more than the tension when the ball is at the top. Find the mass of the ball.

## Homework Equations

Fc=mv^2/r
ac=v^2/r
Equations that have to do with vertical circle

## The Attempt at a Solution

I do not understand vertical circles but I tried doing the Tbottom=Ttop+6mg
I am unsure of the answer but I did 60+Ttop=Ttop+6mg
60=6mg
10=mg
m=1.02 kg
but I think its wrong

## Answers and Replies

jbriggs444
Science Advisor
Homework Helper
Tbottom=Ttop+6mg
Can you explain how you arrived at this equation. In particular, what does the 6mg denote?

Chandra Prayaga
Science Advisor
Draw a diagram showing the forces on the ball at the top and at the bottom of the circle.

• CWatters
gneill
Mentor
You swing a 1.60m long string with a metal ball attached to its end in a vertical circle, such that the speed of the ball does not change but the rope is always taut.
Question: How can the speed not change? What happened to conservation of energy? Is this the exact wording of the original problem?

Chandra Prayaga
Science Advisor
Are there external forces acting on the system? If they are, there is no conservation of energy.

Question: How can the speed not change? What happened to conservation of energy? Is this the exact wording of the original problem?

There would have to be some tangential forces being applied and modulated just so. However there is no law against it, and, assuming these extra forces are truly purely tangential, they don’t prevent you from answering the question. So it’s an unusual construct, but it makes answering the question very easy.