exam1sol - Version 099 – exam1 – markert – (58840) 1...

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Unformatted text preview: Version 099 – exam1 – markert – (58840) 1 This print-out should have 14 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A 0 . 47 kg rock is projected from the edge of the top of a building with an initial velocity of 8 . 56 m / s at an angle 58 ◦ above the horizontal. Due to gravity, the rock strikes the ground at a horizontal distance of 10 . 6 m from the base of the building. Building 10 . 6 m 5 8 ◦ 8 . 5 6 m / s h How tall is the building? Assume the ground is level and that the side of the build- ing is vertical. The acceleration of gravity is 9 . 8 m / s 2 . 1. 10.6934 2. 13.093 3. 5.93437 4. 14.6855 5. 11.9298 6. 6.98248 7. 9.79367 8. 9.9959 9. 8.88269 10. 6.18671 Correct answer: 9 . 79367 m. Explanation: Let : θ = 58 ◦ , v = 8 . 56 m / s , Δ x = 10 . 6 m , and m = 0 . 47 kg . The flying time can be determined by x = v x t t = x v x = x v cos θ . From the point where the rock was projected (set to be the origin O ), the y-coordinate of the point where the rock struck the ground is y = v y t- 1 2 g t 2 = v sin θ parenleftbigg x v cos θ parenrightbigg- 1 2 g parenleftbigg x v cos θ parenrightbigg 2 = x tan θ- g x 2 2 ( v cos θ ) 2 , so h = | y | = g x 2 2 ( v cos θ ) 2- x tan θ = (9 . 8 m / s 2 ) (10 . 6 m) 2 2 [(8 . 56 m / s) cos58 ◦ ] 2- (10 . 6 m) tan58 ◦ = 9 . 79367 m . 002 10.0 points Can an object reverse its direction of travel while maintaining a constant acceleration? 1. No; if the acceleration is constant, the direction of the speed remains unchanged. 2. All are wrong. 3. No; the direction of the speed is always the same as the direction of the acceleration. 4. Yes; a ball tossed upward reverses its di- rection of travel at its highest point. correct 5. Yes; a ball thrown toward a wall bounces back from the wall. Explanation: Velocity and acceleration need not be in the same direction. When a ball is tossed upward Version 099 – exam1 – markert – (58840) 2 it experiences a constant acceleration directed downward. 003 10.0 points A ball is thrown 182 m upward and then falls back to earth. The acceleration of gravity is 9 . 8 m / s 2 ....
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This note was uploaded on 01/08/2010 for the course CH 53675 taught by Professor Bocknack during the Fall '09 term at University of Texas.

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exam1sol - Version 099 – exam1 – markert – (58840) 1...

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