The 1.3 kg balls are attached to the ends of a thin rod of length 52.0 cm and ne
ID: 2289931 • Letter: T
Question
The 1.3 kg balls are attached to the ends of a thin rod of length 52.0 cm and negligible mass. The rod is free to rotate in a vertical plane without friction about a horizontal axis through its center. With the rod initially horizontal (as shown), a 48.0 g wad of wet putty drops onto one of the balls, hitting with a speed of 1.00 m/s and then sticking to it. (a) What is the angular speed of the system just after the putty wad hits? Rad/s (b) What is the ratio of the kinetic energy of the system after the collision to that of the putty wad just before? KEafter/KEbefore = (c) Through what angle will the system rotate before it momentarily stops?Explanation / Answer
This is a conservation of angular momentum problem.
To determine the angular velocity, just after the putty wad hits the ball, we need to know the angular momentum of the putty wad just before it hits the ball.
Angular momentum = moment of inertia * angular velocity
Moment of inertia = (mass of ball) * (perpendicular distance from the axis of rotation)^2
Mass of putty wad = 48 g = 0.048 kg
The perpendicular distance from the axis of rotation is
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