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PHY131_F04_M2_Solutions

# PHY131_F04_M2_Solutions - PHYSICS 131 SECOND MIDTERM...

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PHYSICS 131 SECOND MIDTERM EXAMINATION ------------------------------------------------------------------------- You are allowed to use a calculator, a sheet of formulae, pencils, rulers, erasers. Use of cell phones, computers, books, class notes, TV guides etc. is not allowed. Solve any three of the following four problems. If you attempt/solve four, please indicate clearly on your blue book, which three problems would you like us to consider. All problems carry equal weight. Problem 1: (Use g = 10 m/s 2 in this problem) Ken, a Psychology Major, has hopelessly fallen for Kim. Ken and Kim are skating together on a rink at 3.00 m/s. Ken keeps asking Kim how much she weighs(!). Annoyed, Kim pushes away from Ken while still moving in the same direction and as a result speeds up to 4.00 m/s and Ken slows down to 2.5 m/s. Friction, in the physics sense between the skaters and the ice rink, is negligible in this drama. Being a psychology major, Ken neglected to take Physics 131 and does not know that he has all the information he needs to know the answer to his question. He tells you the story and you offer to help. You ask him and he replies that his weight is 700 N. a) Calculate Kim’s weight. b) If Kim had pushed Ken harder and as a result Ken came to a full stop, calculate Kim’s final velocity? c) Suppose Kim got away at 9.0 m/s and was so happy that she went in to a classic skaters spin: hands close to her body and went in to a spin about the vertical axis passing through the center of her body. Approximating her body to be a solid cylinder of radius 20 cm and moment of inertia I body = 1/2(MR 2 ), calculate the maximum angular velocity ω she could attain using all her translational kinetic energy.

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