Homework 8 Sol. - Abd Elhai, Mohamed – Homework 8 –...

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Unformatted text preview: Abd Elhai, Mohamed – Homework 8 – Due: Apr 7 2008, 9:00 pm – Inst: Dr Kevin Dean 1 This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. This is ONLINE HOMEWORK No. 8 (HW19-OH08). It is due by 06:00 AM Abu Dhabi Time on Tuesday 8 April (9:00 PM Monday 7 April, Texas time). 001 (part 1 of 1) 10 points A 8 kg steel ball strikes a wall with a speed of 12 . 1 m / s at an angle of 49 ◦ with the normal to the wall. It bounces off with the same speed and angle, as shown in the figure. x y 1 2 . 1 m / s 8 kg 1 2 . 1 m / s 8 kg 49 ◦ 49 ◦ If the ball is in contact with the wall for . 106 s, what is the magnitude of the average force exerted on the ball by the wall? Correct answer: 1198 . 24 N. Explanation: Let : M = 8 kg , v = 12 . 1 m / s , and θ = 49 ◦ . 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(8 kg)(12 . 1 m / s) cos49 ◦ . 106 s k ~ F k = 1198 . 24 N . Note: The direction of the force is in negative x direction, as indicated by the minus sign. keywords: 002 (part 1 of 3) 4 points The force of magnitude F x acting in the x direction on a 2 . 5 kg particle varies in time as shown in the figure. 1 2 3 4 5 1 2 3 4 F x (N) t (s) Find the impulse of the force. Correct answer: 6 N · s. Explanation: The impulse is the area under the F versus t graph; i.e , the sum of the area of the rectangle plus two triangles, so Impulse = 2 • (2 N)(2 s) 2 ‚ + (2 N)(1 s) = 6 N · s 003 (part 2 of 3) 3 points Find the final velocity of the particle if it is initially at rest. Correct answer: 2 . 4 m / s. Explanation: Given : m = 2 . 5 kg and v i = 0 m / s . Abd Elhai, Mohamed – Homework 8 – Due: Apr 7 2008, 9:00 pm – Inst: Dr Kevin Dean 2 Impulse = Δ p F Δ t = m ( v f- v i ) m v f = F Δ t + m v i v f = F Δ t m + v i = 6 N · s 2 . 5 kg + 0 m / s = 2 . 4 m / s 004 (part 3 of 3) 3 points Find the final velocity of the particle if it is initially moving along the x axis with a velocity of- 9 m / s. Correct answer:- 6 . 6 m / s. Explanation: Given : v i =- 9 m / s . v f = v i + F Δ t m =- 9 m / s + 6 N · s 2 . 5 kg =- 6 . 6 m / s keywords: 005 (part 1 of 4) 3 points Allison (of mass 40 kg) is coasting in her wagon (of mass 15 kg) at a constant velocity of 6 m / s . She passes her mother, who drops a bag of toys (of mass 2 kg) into the wagon. What will happen to the speed of the wagon? 1. Unable to determine 2. slow down correct 3. speed up 4. remain the same Explanation: p = m v We expect the wagon to slow down. The momentum immediately before and after the drop must be the same, so since the bag of toys adds mass to the wagon, it must slow down in order to conserve momentum....
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This note was uploaded on 02/16/2010 for the course PHYSICS 191262 taught by Professor Najafzadeh during the Spring '09 term at The Petroleum Institute.

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Homework 8 Sol. - Abd Elhai, Mohamed – Homework 8 –...

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