Question

146 2. A ball of mass m = 0.43 kg is attached to a cord and whirled in a vertical circle of radius R = 1.7 m at a constant speed. The ball takes 3.8 sto go around once. Please find the tension T, in the cord, when the ball is at the bottom of the circle and when it is at the top of the circle.

Answer 1

w = 2pi / T = 2pi / 3.8 = 1.6526 rad/s

a)

tension at bottom

T = mg + m r w^2 = 0.43* 9.8 + 0.43* 1.7* 1.6526^2

T = 6.21 N

b)

at top

T = m r w^2 - mg

T = - 2.217 N

negative sign indicates that, at the top position there is no tension on the string, as it is impossible to rotate the mass vertically with such a low velocity

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