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Unformatted text preview: boland (kbb544) HW7 mackie (10611) 1 This print-out should have 17 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 An animal-rescue plane flying due east at 46 m / s drops a bale of hay from an altitude of 73 m . The acceleration due to gravity is 9 . 81 m / s 2 . If the bale of hay weighs 164 N , what is the momentum of the bale the moment it strikes the ground? Correct answer: 995 . 824 kg m / s. Explanation: Let : v plane = 46 m / s , h = 73 m , and W = 164 N . v plane v 73 m The bale strikes the ground at an angle, so its final velocity v will have both a horizontal and a vertical component, and v 2 = v 2 + v 2 h Vertically, conservation of energy gives us E kf = E po 1 2 mv 2 = mg h v 2 = 2 g h The horizontal component of the bale is v , the speed of the plane, so the speed of the bale as it strikes the ground is v = radicalBig v 2 + v 2 plane = radicalBig 2 g h + v 2 plane The momentum of the bale is thus p = mv = W g radicalBig 2 g h + v 2 plane = 164 N 9 . 81 m / s 2 radicalBig 2 (9 . 81 m / s 2 ) (73 m) + (46 m / s) 2 = 995 . 824 kg m / s . 002 (part 2 of 2) 10.0 points At what angle of inclination will the bale strike? Answer between 180 and +180 . Correct answer: 39 . 4449 . Explanation: When the bale strikes the ground, the ver- tical component is the side opposite the angle of inclination and the horizontal component is the side adjacent, so tan = v v plane = arctan parenleftbigg v v plane parenrightbigg = arctan parenleftbigg 2 g h v plane parenrightbigg = arctan parenleftBigg radicalbig 2 (9 . 81 m / s 2 ) (73 m) 46 m / s parenrightBigg = 39 . 4449 . keywords: 003 10.0 points A child bounces a 60 g superball on the side- walk. The velocity change of the superball is from 22 m / s downward to 15 m / s upward. If the contact time with the sidewalk is 1 800 s, what is the magnitude of the average force exerted on the superball by the sidewalk? boland (kbb544) HW7 mackie (10611) 2 Correct answer: 1776 N. Explanation: Let : m = 60 g = 0 . 06 kg , v u = 15 m / s , v d = 22 m / s , and t = 0 . 00125 s Choose the upward direction as positive. The impulse is I = F t = P = mv u m ( v d ) = m ( v u + v d ) F = m ( v u + v d ) t = (60 g) (15 m / s + 22 m / s) . 00125 s = 1776 N . 004 (part 1 of 2) 10.0 points A revolutionary war cannon, with a mass of 2270 kg, fires a 16 . 5 kg ball horizontally. The cannonball has a speed of 137 m / s after it has left the barrel. The cannon carriage is on a flat platform and is free to roll horizontally. What is the speed of the cannon immedi- ately after it was fired?...
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This note was uploaded on 02/20/2011 for the course PHYS 1062 taught by Professor Mackie during the Spring '11 term at Temple.
- Spring '11