- #1
carl87
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Homework Statement
A ball (mass m = 250 g) on the end of an ideal string is moving in a circular motion as a conical pendulum. The length L of the string is 1.84 m and the angle with the vertical is 37 degrees.
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
Homework Equations
L = m * v * r (where L = momentum)
F centripetal = (mv^2) / r
weight = mg
torque = r vector x F vector
The Attempt at a Solution
For A I assumed the torque was 0 because there wasn't any said force. This obviously was wrong but I do not know why.
For B I used L = m*v*r where L = momentum
First I drew out the diagram.
I noticed r = L * sin 37
I noticed m*g*tan 37 = (m * v^2 /r)
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
Plug and chug:
L = .791 This was incorrect.
Please help!
Thanks