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# solution_pdf5 - billing(cab4763 HW 4 Opyrchal(11109 This...

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billing (cab4763) – HW 4 – Opyrchal – (11109) 1 This print-out should have 12 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A person of mass 77 . 9 kg escapes from a burn- ing building by jumping from a window situ- ated 34 . 2 m above a catching net. The acceleration of gravity is 9 . 8 m / s 2 . If air resistance exerts a force of 104 . 8 N on him as he falls, determine his speed just before he hits the net. Correct answer: 24 . 0479 m / s. Explanation: The forces acting on him are the gravita- tional force m g acting downward, and the air resistance, F a , acting upward. The accelera- tion is downward and the net force is F net = m a = m g - F a a = m g - F a m The person is in free fall, so his final speed is defined by v f = 2 a h = radicalbigg 2 ( m g - F a ) h m = radicalBigg 2 [(77 . 9 kg)(9 . 8 m / s 2 ) - 104 . 8 N] (34 . 2 m) 77 . 9 kg = 24 . 0479 m / s . 002 (part 1 of 3) 10.0 points A boat moves through the water with two forces acting on it. One is a 2271 N forward push by the motor on the propeller, and the other is an 2018 N resistive force due to the water around the bow. What is the acceleration of the 1167 kg boat? Correct answer: 0 . 216795 m / s 2 . Explanation: Given : F 1 = 2271 N , F 2 = 2018 N , and m = 1167 kg . 2271 N 2018 N The forces are unbalanced, so the net force is F net = m a = F 1 - F 2 and a = F 1 - F 2 m = 2271 N - 2018 N 1167 kg = 0 . 216795 m / s 2 forward. 003 (part 2 of 3) 10.0 points If it starts from rest, how far will it move in 17 . 7 s? Correct answer: 33 . 9599 m. Explanation: Given : Δ t = 17 . 7 s Under acceleration, Δ x = v i t + 1 2 a t ) 2 = 1 2 a t ) 2 since v i = 0 m/s. Thus Δ x = 1 2 a t ) 2 = 1 2 ( 0 . 216795 m / s 2 ) (17 . 7 s) 2 = 33 . 9599 m .

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