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Practice Questions for Exam 1-solutions

Practice Questions for Exam 1-solutions - markowitz(am45362...

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markowitz (am45362) – Practice Questions for Exam 1 – distler – (56295) 1 This print-out should have 11 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points A freight train has a mass of 2 . 5 × 10 7 kg. If the locomotive can exert a constant pull of 5 . 4 × 10 5 N, how long would it take to increase the speed of the train from rest to 89 . 2 km / h? Disregard friction. Correct answer: 1147 . 12 s. Explanation: Let : m = 2 . 5 × 10 7 kg F net = 5 . 4 × 10 5 N v f = 89 . 2 km / h vector F net = summationdisplay vector F = mvectora a = F net m = 5 . 4 × 10 5 N 2 . 5 × 10 7 kg = 0 . 0216 m / s 2 . Since v i = 0 m/s, v f = a t Δ t = v f a = 89 . 2 km / h 0 . 0216 m / s 2 · 1000 m 1 km · 1 h 3600 s = 1147 . 12 s . 002 10.0points The horizontal surface on which the objects slide is frictionless. The acceleration of gravity is 9 . 8 m / s 2 . 1 kg 9 kg 4 kg F F r If F = 20 N and F r = 6 N, what is the magnitude of the force exerted on the block with mass 9 kg by the block with mass 4 kg? Correct answer: 10 N. Explanation: m 1 m 2 m 3 F F r Given : vector F = +20 N ˆ ı , vector F r = 6 N ˆ ı , m 1 = 1 kg , m 2 = 9 kg , m 3 = 4 kg , and g = 9 . 8 m / s 2 . Note: F is acting on the combined mass of the three blocks, resulting in a common acceleration after accounting for friction. m 1 F 21 F m 2 F 32 F 12 m 3 F r F 23 Let F , F r , F 32 represent the force exerted on the system from the right, from the left, and the force exerted on m 2 by m 3 , respec- tively. Note: vector F 21 = vector F 12 and vector F 32 = vector F 23 , and bardbl vector F 21 bardbl = bardbl vector F 12 bardbl and bardbl vector F 32 bardbl = bardbl vector F 23 bardbl , where bardbl vector F bardbl ≡ F is the magnitude of vector F .

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