angular momentum

[guru]

This problem is baffling me.

A 3kg puck revolves in a circle on a frictionless table at the end of a 50cm long string. The puck's angular momentum is 3kg (m^2/s). What is the tension in the string?

This what I did
L= mrv
therefore
3kg*.25m*v = 3kgm^2/2
v=4m/s
F=(mv^2)/r
(3kg*16m/s)/(.25m) = 192N

is this right?

[arildno]

r should be 0.50 m, not 0.25.

[MiGUi]

I agree with arildno, the string is acting as the radius of the circle itself, not as the diameter :smile:

[Doc Al]

Once again: Do not double post!
http://www.physicsforums.com/showthread.php?t=50626