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11 - roofner(bar784 Homework 11 Weathers(17104 This...

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roofner (bar784) – Homework 11 – Weathers – (17104) 1 This print-out should have 10 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A 5 kg steel ball strikes a wall with a speed of 5 . 18 m / s at an angle of 34 . 4 with the normal to the wall. It bounces off with the same speed and angle, as shown in the figure. x y 5 . 18 m / s 5 kg 5 . 18 m / s 5 kg 34 . 4 34 . 4 If the ball is in contact with the wall for 0 . 209 s, what is the magnitude of the average force exerted on the ball by the wall? Correct answer: 204 . 502 N. Explanation: Let : M = 5 kg , v = 5 . 18 m / s , and θ = 34 . 4 . The y component of the momentum is un- changed. The x component of the momentum is changed by Δ P x = 2 M v cos θ . Therefore, using impulse formula, F = Δ P Δ t = 2 M v cos θ Δ t = 2 (5 kg) (5 . 18 m / s) cos 34 . 4 0 . 209 s bardbl vector F bardbl = 204 . 502 N . Note: The direction of the force is in negative x direction, as indicated by the minus sign. 002 10.0 points A golf ball ( m = 28 . 6 g) is struck a blow that makes an angle of 58 with the horizontal. The drive lands 199 m away on a flat fairway. The acceleration of gravity is 9 . 8 m / s 2 . If the golf club and ball are in contact for 7 . 59 ms, what is the average force of impact? Neglect air resistance. Correct answer: 175 . 523 N. Explanation: Let : g = 9 . 8 m / s 2 , m = 28 . 6 g , θ = 58 , and t = 7 . 59 ms . Note that the range of the golf ball is given by L = v 2 sin 2 θ g , so the initial velocity of the ball is v 0 = radicalBigg L g sin(2 θ ) = radicalBigg (199 m) (9 . 8 m / s 2 ) sin(2 × 58 ) = 46 . 5811 m / s . The average force exerted is the change in its momentum over the time of contact F = m v 0 t = (28 . 6 g) (0 . 001 kg / g) (46 . 5811 m / s) (7 . 59 ms) (0 . 001 s / ms) = 175 . 523 N . 003 10.0 points A 1 . 35 kg particle has a velocity of v x = 2 . 29 m / s and v y = 3 . 62 m / s. Find the magnitude of its total momen- tum. Correct answer: 5 . 78275 kg · m / s. Explanation:
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roofner (bar784) – Homework 11 – Weathers – (17104) 2 Let : m = 1 . 35 kg , v x = 2 . 29 m / s , and v y = 3 . 62 m / s .
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