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Swinging rod

A wooden rod of negligible mass and length 80.0 cm is pivoted about a horizontal axis through its center. A white rat with mass 0.550 kg clings to one end of the stick, and a mouse with mass 0.170 kg clings to the other end. The system is released from rest with the rod horizontal.

If the animals can manage to hold on, what are their speeds as the rod swings through a vertical position?

Solution Preview

On the stick you have a mass of m1= 0.550 kg on one end and a mass of m2 = 0.170 kg on the other end. The side where m1 hangs on is heavier and will thus swing downward. You can find the velocity when the rod is vertical by using conservation of energy.

The increase in kinetic energy must equal the ...

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