(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A 0.2kg ball and its supporting cord are revolving about the vertical axis on the fixed smooth conical surface with an angular velocity of 4 rad/s. The ball is held in the position b=0.3m by the tension T in the cord. If the distance b is reduced to the constant value of 0.2m by increasing the tension T in the cord, compute the new angular velocity w and the work done on the system by T.

2. Relevant equations

[tex]\sum[/tex]M=dH/dt

H=r x mv

3. The attempt at a solution

I solved this problem using conservation of angular momentum and it came out correct, but I can't for the life of me understand why momentum is conserved. I understand that the force in the radial direction does not have a moment about the radial direction because the cross product is zero, but what about the vertical direction? Doesn't the ball have to accelerate in the vertical direction in order to change its b value from 0.3 to 0.2? And doesn't an acceleration in the vertical direction mean an unbalanced force in the vertical direction, which subsequently means having an unbalanced moment about the middle of the cone?

Please let me know if I'm not making sense.

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# Homework Help: Problem using conservation of angular momentum

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