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Unformatted text preview: karna (pk4534) HW 9 coker (58245) 1 This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. I could find very few problems in the bank that were relevant to Ch. 10 in Ohanian and Markert. 001 (part 1 of 2) 10.0 points An object is moving so that its kinetic energy is 95 . 4 J and the magnitude of its momentum is 47 . 8 kg m / s. Determine the speed of the object. Correct answer: 3 . 99163 m / s. Explanation: Let : K = 95 . 4 J and p = 47 . 8 kg m / s . The kinetic energy is given by K = 1 2 mv 2 , and the magnitude of the momentum is p = mv. Dividing one equation by the other yields K p = v 2 . v = 2 K p = 2 (95 . 4 J) 47 . 8 kg m / s = 3 . 99163 m / s . 002 (part 2 of 2) 10.0 points Determine the mass of the object. Correct answer: 11 . 9751 kg. Explanation: m = p v = 47 . 8 kg m / s 3 . 99163 m / s = 11 . 9751 kg . 003 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. Down with a speed less than v correct 2. Up with speed v 3. Down with speed v 4. Up with a speed less than v 5. The balloon does not move. 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. 004 10.0 points Two blocks of masses m and M [ M = 2 . 45 m ] are placed on a horizontal, frictionless surface. A light spring is attached to one of them, and the blocks are pushed together with the spring between them. A cord holding them together is burned, after which the block of mass M moves to the right with a speed of 2 . 01 m / s. karna (pk4534) HW 9 coker (58245) 2 m M m M Before After (a) (b) v What is the speed of the block of mass m ? Correct answer: 4 . 9245 m / s. Explanation: From conservation of momentum p = 0, in our case we obtain 0 = M v M mv m . Therefore v m = M m v M = (2 . 45) v M = (2 . 45) (2 . 01 m / s) = 4 . 9245 m / s . 005 10.0 points A baseball player uses a pitching machine to help him improve his batting average. He places the 77 kg machine on a frozen pond. The machine fires a 0 . 153 kg baseball horizon- tally at a speed of 36 . 8 m / s. What is the magnitude of the recoil velocity of the machine?...
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This note was uploaded on 10/29/2009 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas at Austin.
- Spring '08