Practice_exam_3_key

# Practice_exam_3_key - 1 We apply the angular momentum...

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1) We apply the angular momentum principle! System: Stick Surroundings: Ice, Earth, Person Initial state: Stick at rest before force of the person is applied Final state: After the force has been applied and the stick is rotating The normal force from the ice and the gravitational force due to the interaction with the earth cancel. Furthermore, note that we will approximate the ice as being frictionless. 2 2 0, , 0 25, 0, 0 2 12 150 ˆ 500 sys net net L t I t I const r F t I L ML t z t ML rad t s 2) Let’s use the point particle view of the situation. System: The massless string and the two disks Surroundings: The person applying the force, the frictionless surface, and the Earth Initial: Before the pull when the disks are not touching Final: After the pull when the disks are touching. The normal force from the surface and the gravitational force due to the interaction with the earth cancel. net pull F F

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