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April 20, 2014

April 20, 2014

Posted by **Joe** on Wednesday, July 11, 2012 at 7:48pm.

a) What is the magnitude of the torque (N m) exerted on the ball about the support point?

b) What is the magnitude of the angular momentum (kg m^2/2) of the ball about the support point?

Correct Answers: a) 2.71 b) 1.32

For a I assumed 0 because there wasn't any said force. I do not know how to solve problem.

For b I used L = m*v*r where L = momentum

m = .250 kg

v = (r * g * tan 37 )^(0.5) = (L*sin 37*9.8*tan 37)^(0.5) = 2.8596

r = L * sin 37 = 1.84 * sin 37= 1.10733

Therefore L = .791 This was supposedly incorrect

- Physics -
**drwls**, Thursday, July 12, 2012 at 7:20ama) The weight exerts a torque about the support point. It equals

Torque = M g L sin37 = 2.71 N*m^2

I am using the symbol L for string length

b) First, get the rotation period P of the ball, using equations derived at

http://en.wikipedia.org/wiki/Conical_pendulum

P = 2 pi sqrt(L cos37/g) = 2.43 seconds

Ball's speed V = 2 pi L sin37/P = 2.86 m/s

The angular momentum about the support point is M*V*L

= 0.25*2.86 * 1.84 = 1.32 kg*m^2/s.

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