Ball on a string (vertical circle)

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Homework Statement

a 500 g ball moves in a vertical circle on a 1.01 m long string. if the speed at the top is 4.3 m/s, then the speed at the bottom will be 7.62 m/s. what is the tension of the string when the ball is at the top? when is the tension of the string when the ball is at the bottom?

Homework Equations

tension = (F_net)=mv²/r

The Attempt at a Solution

top:
tension = (F_net)=(0.5 kg)(4.3)²/(1.01) = 9.15 N

bottom:
tension = (F_net)=(0.5 kg)(7.62)²/(1.01) = 28.7 N

these answers are wrong, however. and I'm not exactly sure why.
pointers in the right direction would be much appreciated!

 

[Engineering_PHY123]

The numbers you found were the magnitudes of the force pointing directly outward from the string, but that is not the tension in the string. Use the gravitational force on the ball to solve for the tension in the trope. Drawing a force diagram will make this problem more understandable.

 

[jim mcnamara]

@Engineering_PHY123 - this thread was started more than 11 years ago. The OP has not visited PF for more than 10 years.