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Unformatted text preview: kaplan (hmk378) – Homework 12 – Weathers – (17104) 1 This printout should have 10 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A 3 kg steel ball strikes a wall with a speed of 12 . 8 m / s at an angle of 55 . 4 ◦ with the normal to the wall. It bounces off with the same speed and angle, as shown in the figure. x y 1 2 . 8 m / s 3 kg 1 2 . 8 m / s 3 kg 55 . 4 ◦ 55 . 4 ◦ If the ball is in contact with the wall for . 206 s, what is the magnitude of the average force exerted on the ball by the wall? Correct answer: 211 . 701 N. Explanation: Let : M = 3 kg , v = 12 . 8 m / s , and θ = 55 . 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 (3 kg) (12 . 8 m / s) cos 55 . 4 ◦ . 206 s bardbl vector F bardbl = 211 . 701 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 = 56 . 4 g) is struck a blow that makes an angle of 51 . 6 ◦ with the horizontal. The drive lands 201 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 . 06 ms, what is the average force of impact? Neglect air resistance. Correct answer: 359 . 335 N. Explanation: Let : g = 9 . 8 m / s 2 , m = 56 . 4 g , θ = 51 . 6 ◦ , and t = 7 . 06 ms . Note that the range of the golf ball is given by L = v 2 sin2 θ g , so the initial velocity of the ball is v = radicalBigg L g sin(2 θ ) = radicalBigg (201 m) (9 . 8 m / s 2 ) sin(2 × 51 . 6 ◦ ) = 44 . 9806 m / s . The average force exerted is the change in its momentum over the time of contact F = mv t = (56 . 4 g) (0 . 001 kg / g) (44 . 9806 m / s) (7 . 06 ms) (0 . 001 s / ms) = 359 . 335 N . 003 10.0 points A 3 . 66 kg particle has a velocity of v x = 1 . 62 m / s and v y = − 2 . 59 m / s. kaplan (hmk378) – Homework 12 – Weathers – (17104) 2 Find the magnitude of its total momentum....
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This document was uploaded on 10/26/2011 for the course PHYS 1710 at North Texas.
 Fall '08
 Weathers
 mechanics, Work

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