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Unformatted text preview: khounvivongsy (sk27799) Homework 6 Weathers (17104) 1 This printout should have 10 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 (part 1 of 2) 10.0 points A car travels due east with a horizontal speed of 52 . 3 km / h. Rain is falling vertically with respect to Earth. The traces of the rain on the side windows of the car make an angle of 69 . 6 with the vertical. Find the magnitude of the velocity of the rain with respect to the car. Correct answer: 55 . 7996 km / h. Explanation: Taking down and west be positive, let v ce = velocity of car relative to Earth, v rc = velocity of rain relative to car, and v re = velocity of rain relative to Earth. Given : v ce = 52 . 3 km / h and = 69 . 6 . The car is moving out from under the rain, so the rain streaks are westward toward the rear bumper. v r c 52 . 3 km / h v re 69 . 6 Note: Figure is not drawn to scale sin = v ce v rc v rc = v ce sin = 52 . 3 km / h sin 69 . 6 = 55 . 7996 km / h at 69 . 6 west of vertical. 002 (part 2 of 2) 10.0 points Find the magnitude of the rains velocity with respect to Earth. Correct answer: 19 . 4502 km / h. Explanation: cos = v re v rc v re = v rc cos = (55 . 7996 km / h) cos69 . 6 = 19 . 4502 km / h . 003 10.0 points A boat moves through the water of a river at 12 m / s relative to the water, regardless of the boats direction. If the current is flowing at 9 . 13 m / s, how long does it take the boat to complete a trip consisting of a 475 m displacement down stream followed by a 197 m displacement up stream? Correct answer: 91 . 121 s. Explanation: Let v b be the velocity of the boat relative to the water, and v w the velocity of water relative to the shore. Take downstream as the positive direction. For the downstream trip, the current is speeding him up, so the velocity of the boat relative to the shore is v d = v b + v w and the time is t d = x d v d = x d v b + v w For the upstream trip, the current is slowing him down, so the velocity of the boat relative to the shore is v u = v b v w and the time is t u = x u v u = x u v...
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 Spring '09
 weathers
 Physics

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