Physics
posted by Emily Grossman on .
How do you solve this problem?
A ball on the end of a string is revolved at a uniform rate in a vertical circle radius of 72.0 cm, as shown in figure. If its speed is 4.00m/s and its mass is .300 kg. Calculate the tension in the string when the ball is a) at the top of the path, and b). when it's at the bottom?

a) Mg + T = MV^2/R
T = M(V^2/R g)
b) T  Mg = MV^2/R
T = M(V^2/R + g)
T is the tension that you want to compute.
Make sure R is in meters when you do the calculation. The force will be in Newtons. 
Can you like work the problem out so i can see how it is done?

what is the V in this case? That's what throwing me off..

V is velocity, given as 4m/s

Okay, I worked them out, but I am not getting the answer they should be. Like a) i am getting as what should be the answer as b. So, i don't if someone could work them out or tell me maybe what doing wrong. Thanks!

If the answers to a and b answers are interchanged, your book may be wrong.
All you have to do is use the formulas provided, using these variables:
V = 4.0 m/s
M = 0.3 kg
g = 9.8 m/s^2
R = 0.72 m 
Okay, so for a) get 3.13 and b). get 16.5?