Consider a 8·kg ball with a radius of 0.5·m and rotating about an axis passing t
ID: 1372098 • Letter: C
Question
Consider a 8·kg ball with a radius of 0.5·m and rotating about an axis passing through its center. (a) What is its rotational inertia? kg·m2 (b) Suppose the ball is rotating counterclockwise and slowing down with a rotational acceleration of 4·rad/s2. What is the net torque acting on the ball? N·m direction? clockwise counterclockwise (c) Suppose the torque you found for the last part is being produced by a force applied at a point 0.3·m from the axis. If the direction of the force is perpendicular to a line from the axis to that point, what is the magnitude of the force? N
Explanation / Answer
a) Icm = (2/5)*M*R^2
= (2/5)*8*0.5^2
= 0.8 kg.m^2
b) Net torque, Tnet = I*alfa
= 0.8*4
= 3.2 N.m
c) Tnet = r*F*sin(90)
F = Tnet/r
= 3.2/0.3
= 10.67 N
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