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Unformatted text preview: madrid (tmm2353) – HW #13 – Antoniewicz – (56445) 1 This printout should have 27 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 2) 5.0 points Powerful sports cars can go from zero to 25 m/s (about 60 mph) in 5 seconds. What is the magnitude of the acceleration? Answer in m / s 2 . Correct answer: 5 m / s 2 . Explanation: To find the magnitude of a constant accel eration, we can simply create the following ratio: v final − v inital t final − t initial = 25 m / s − 5 s − = 5 m / s 2 . 002 (part 2 of 2) 5.0 points How does this compare with the acceleration of a falling rock? 1. It is much greater than the acceleration of a falling rock. 2. It is much less than the acceleration of a falling rock. 3. It is about half the acceleration of a falling rock. correct 4. It is about twice the acceleration of a falling rock. 5. The acceleration of a falling rock increases as it falls, so the question is not meaningful. 6. The two accelerations are about the same. Explanation: Objects near the surface of the earth all fall at g ≈ 10 m / s 2 . Therefore the car’s acceleration is about half that of a falling rock. 003 (part 1 of 2) 5.0 points A tennis ball of mass 57 g travels with velocity vectorv i = ( 51 , , ) m / s toward a wall. After bouncing off the wall, the tennis ball is observed to be traveling with velocity vectorv f = (− 44 , , ) m / s . vectorv i vectorv f Before After Notice that this ball only has motion in the x direction, so the change in momentum will be of the form Δ vectorp = ( Δ vectorp x , , ) . Find Δ vectorp x . Answer in kg · m / s. Correct answer: − 5 . 415 kg · m / s. Explanation: To find the change in momentum, we pro ceed as follows: Δ vectorp = vectorp f − vectorp i = mvectorv f − mvectorv i = m ( vectorv f − vectorv i ) = m ( (− 44 , , ) m / s − ( 51 , , ) m / s) = (0 . 057 kg) × (− 95 , , ) m / s = (− 5 . 415 , , ) kg · m / s . So Δ vectorp x = − 5 . 415 kg · m / s 004 (part 2 of 2) 5.0 points What is the change in the magnitude of the tennis ball’s momentum? Answer in kg · m / s. Correct answer: − . 399 kg · m / s. Explanation: Remember that magnitude refers only to the length of a vector, not its direction. So if madrid (tmm2353) – HW #13 – Antoniewicz – (56445) 2 we want the change in magnitude, we need to take the magnitudes of vectorp i and vectorp f and find the change. We would usually use the Pythagorean theorem to find the magnitude of a vector, but in this case, our vectors have only one component each, so finding the mag nitudes is easy. For vectorp i ,  vectorp i  =  (0 . 057 kg) × ( 51 , , ) m / s  = ( 2 . 907 , , ) kg · m / s  = 2 . 907 kg · m / s ....
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 Fall '08
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