Teaching Physics with the Physics Suite

Edward F. Redish

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Cat on a ladder

Two workmen are carrying a 6 meter ladder as shown in the sketch below. The ladder has a mass of 15 kilograms. A cat, with a mass of 5 kg, jumps on the ladder and hangs on, 1 meter from the end of the ladder. How much force does each workman have to exert to hold the ladder up?

Note to the instructor: Although this seems like a pretty trivial problem, it is a good one to get students thinking about the meaning of torque and how it relates to their personal experience. I often use this problem before I've introduced torque and define it by building on students' intuitions about what should happen in this case.

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Page last modified December 4, 2004: R24