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Unformatted text preview: zhou (cz3574) – 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 52 m / s drops a bale of hay from an altitude of 89 m . The acceleration due to gravity is 9 . 81 m / s 2 . If the bale of hay weighs 176 N , what is the momentum of the bale the moment it strikes the ground? Correct answer: 1196 . 83 kg m / s. Explanation: Let : v plane = 52 m / s , h = 89 m , and W = 176 N . v plane v ⊥ θ 89 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 = 176 N 9 . 81 m / s 2 × radicalBig 2 (9 . 81 m / s 2 ) (89 m) + (52 m / s) 2 = 1196 . 83 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: 38 . 7855 ◦ . 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 θ = v ⊥ v plane θ = arctan parenleftbigg v ⊥ v plane parenrightbigg = arctan parenleftbigg √ 2 g h v plane parenrightbigg = arctan parenleftBigg radicalbig 2 (9 . 81 m / s 2 ) (89 m) 52 m / s parenrightBigg = 38 . 7855 ◦ . keywords: 003 10.0 points A child bounces a 53 g superball on the side- walk. The velocity change of the superball is from 22 m / s downward to 17 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? zhou (cz3574) – HW7 – mackie – (10611) 2 Correct answer: 1653 . 6 N. Explanation: Let : m = 53 g = 0 . 053 kg , v u = 17 m / s , v d = 22 m / s , and Δ t = 0 . 00125 s Choose the upward direction as positive. The impulse is I = F Δ t = Δ P = mv u − m ( − v d ) = m ( v u + v d ) F = m ( v u + v d ) Δ t = (53 g) (17 m / s + 22 m / s) . 00125 s = 1653 . 6 N . 004 (part 1 of 2) 10.0 points A revolutionary war cannon, with a mass of 2170 kg, fires a 16 kg ball horizontally. The cannonball has a speed of 109 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 03/25/2011 for the course PHYS 122 taught by Professor Hiyishi during the Spring '10 term at Temple College.
- Spring '10