Dr. O. stands on a skateboard at rest. Bingley throws a heavy ball at him. What

Question

Dr. O. stands on a skateboard at rest. Bingley throws a heavy ball at him. What should Dr. O, do to the ball to maximize his speed on the skateboard after the interaction? Consider the following 4 objects rotating about the point P. Each has mass distributed uniformly in the grey regions, and each object has the same total mass. Which has the largest moment of inertia? The center of mass of the system made up of the Earth and the Sun Dr. O, hits a fly with a fly-swatter. Which statement is true about the collision?

Explanation / Answer

1) To have a greater change in momentum ( impulse ), Dr. O should reflect the ball in the same initial direction. Deflect the ball back to Bingley.

2) Considering the mass to be same the moment of inertia is

moment of inertia of the first diagram I1 = (1/2) M r^2

moment of inertia of the second diagram I2 = (2/5) M R^2

moment of inertia of the third diagram I3 = (1/3) M R^2

moment of inertia of the fourth diagram I4 = (1/12) M R^2

It is clear that the moment of inertia of the spoked wheel is larger.

3) the center of mass will be closer to the heavier object. Sun is heavier than earth so the center of mass will be closer to the sun than earth.

4) During collision the force is equal and opposite but the acceleration of the fly is higher than the swatter. The impulse is same so is the momentum but the speed of the fly is higher than speed of the swatter after collision.

None of hte above.

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