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Unformatted text preview: reddy (ar38357) Collisions clancy (SCI411-2) 1 This print-out should have 9 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points A balloon of mass M is floating motionless in the air. A person of mass less than M is on a rope ladder hanging from the balloon. The person begins to climb the ladder at a uniform speed v relative to the ground. How does the balloon move relative to the ground? 1. Up with a speed less than v 2. Up with speed v 3. The balloon does not move. 4. Down with a speed less than v correct 5. Down with speed v Explanation: Let the mass of the person be m . Total momentum is conserved (because the exterior forces on the system are balanced), especially the component in the vertical di- rection. When the person begins to move, we have mv + M v M = 0 , = v M =- m M v < v = | v M | = m M v < v, since m < M = m M < 1 . Thus the balloon moves in the opposite direction. 002 10.0 points A tennis player places a 63 kg ball machine on a frictionless surface. The machine fires a 0.054 kg tennis ball horizontally with a veloc- ity of 42 m / s toward the north. What is the final velocity of the machine? Correct answer:- . 036 m / s. Explanation: Let north be positive. Let : m 1 = 63 kg , m 2 = 0 . 054 kg , and v 2 ,f = 42 m / s ....
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