05 - fryer (vdf96) Assignment 4 Friction and Statics graves...

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fryer (vdf96) – Assignment 4 Friction and Statics – graves – (6) 1 This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page – ±nd all choices before answering. 001 (part 1 of 2) 10.0 points A child holds a sled on a frictionless, snow- covered hill, inclined at an angle of 31 . 82 N F 31 If the sled weighs 82 N, ±nd the force ex- erted on the rope by the child. Correct answer: 42 . 2331 N. Explanation: Given : W = 82 N and θ = 31 . Consider the free body diagram for the block mg sin θ N = cos W Basic Concepts: If we “tilt” our world, and consider the forces parallel to the hill, F net = s F up - s F down = 0 then the forces perpendicular to the hill, F net = s F out - s F in = 0 Solution: Consider the free body diagram for the sled: The weight of the sled has compo- nents W sin θ acting down the hill and W cos θ acting straight into the hill. The system is in equilibrium, so for forces parallel to the hill, F net = T -W sin θ = 0 = T = W sin θ = (82 N) sin31 = 42 . 2331 N 002 (part 2 of 2) 10.0 points What force is exerted on the sled by the hill? Correct answer: 70 . 2877 N. Explanation: For forces perpendicular to the hill, F net = N -W cos θ = 0 = ⇒ N = W cos θ = (82 N) cos31 = 70 . 2877 N 003 (part 1 of 2) 10.0 points WITHDRAWN 004 (part 2 of 2) 10.0 points WITHDRAWN 005 (part 1 of 2) 10.0 points WITHDRAWN 006 (part 2 of 2) 10.0 points WITHDRAWN 007 10.0 points If only an external force can change the veloc- ity of a body, how can the internal force of the brakes bring a car to rest? 1. It is the driver, not the car itself who causes the breaking, so it is an external force. 2. Some internal forces can change the ve- locity of a body.
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fryer (vdf96) – Assignment 4 Friction and Statics – graves – (6) 2 3. The engine is stopped, so the car has no force to run further. 4.
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This note was uploaded on 12/11/2011 for the course PHYSICS 101 taught by Professor Graves during the Fall '10 term at San Jose City College.

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05 - fryer (vdf96) Assignment 4 Friction and Statics graves...

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