# exam1sol - Version 099 exam1 markert(58840 This print-out...

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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 58 8 . 56 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 0 = 8 . 56 m / s , Δ x = 10 . 6 m , and m = 0 . 47 kg . The flying time can be determined by x = v 0 x t t = x v 0 x = x v 0 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 0 y t - 1 2 g t 2 = v 0 sin θ parenleftbigg x v 0 cos θ parenrightbigg - 1 2 g parenleftbigg x v 0 cos θ parenrightbigg 2 = x tan θ - g x 2 2 ( v 0 cos θ ) 2 , so h = | y | = g x 2 2 ( v 0 cos θ ) 2 - x tan θ = (9 . 8 m / s 2 ) (10 . 6 m) 2 2 [(8 . 56 m / s) cos 58 ] 2 - (10 . 6 m) tan 58 = 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

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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 . t h A y t B h B t A v 0 O B A t A is the time to reach its maximum height h A Figure is not drawn to scale.
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