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PHY303k_-_Spring_2010_-_HW_12 - saldana(avs387 Homework 12...

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saldana (avs387) – Homework 12 – florin – (58140) 1 This print-out should have 8 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 2) 10.0 points The coefficient of friction is μ from A to B, and B to E is frictionless. Block m 1 is pushed down the ramp and released at A with velocity v 1 and is accelerating down. Let E = K + U = mechanical energy vector P = momentum A B C D E m 1 m 2 What is conserved as m 1 goes from A to B? 1. Neither E nor vector P correct 2. E 3. Both E and vector P 4. vector P Explanation: Because there is friction, energy is dissi- pated and mechanical energy is not conserved. Because there is gravity as well as friction and the net force is not zero since it is accelerating down, momentum is not conserved. 002 (part 2 of 2) 10.0 points What is conserved as the masses m 1 + m 2 slide together from D to E? 1. Both E and vector P 2. Neither E nor vector P 3. E correct 4. vector P Explanation: Because there is no friction between the track and the masses, the mechanical energy E is conserved. But the total momentum vector P is not conserved because the magnitude and direction of the velocity of the masses change due to the gravity and the normal force by the track. 003 10.0 points A triangular wedge 5 m high, 12 m base length, and with a 14 kg mass is placed on a frictionless table. A small block with a 6 kg mass (and negligible size) is placed on top of the wedge as shown in the figure below. 14 kg 12 m 5 m 6 kg Δ X wedge 14 kg 12 m 5 m 6 kg All surfaces are frictionless, so the block slides down the wedge while the wedge slides sidewise on the table. By the time the block slides all the way down to the bottom of the wedge, how far Δ X wedge does the wedge slide to the right? Correct answer: 3 . 6 m. Explanation: Let : M = 14 kg , m = 6 kg , L = 12 m , and H = 5 m .
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saldana (avs387) – Homework 12 – florin – (58140) 2 Consider the wedge and the block as a two- body system. The external forces acting on this system — the weight of the wedge, the weight of the block and the normal force from the table — are all vertical, hence the net hor- izontal momentum
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