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Unformatted text preview: louey (cal2859) – Ch1-H3 – florin – (56930) 1 This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 2) 10.0 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) 10.0 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. The two accelerations are about the same. 4. It is about twice the acceleration of a falling rock. 5. It is about half the acceleration of a falling rock. correct 6. The acceleration of a falling rock increases as it falls, so the question is not meaningful. 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) 10.0 points A tennis ball of mass 57 g travels with velocity vectorv i = ( 48 , , ) m / s toward a wall. After bouncing off the wall, the tennis ball is observed to be traveling with velocity vectorv f = (− 45 , , ) 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 . 301 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 ( (− 45 , , ) m / s − ( 48 , , ) m / s) = (0 . 057 kg) × (− 93 , , ) m / s = (− 5 . 301 , , ) kg · m / s . So Δ vectorp x = − 5 . 301 kg · m / s 004 (part 2 of 2) 10.0 points What is the change in the magnitude of the tennis ball’s momentum? Answer in kg · m / s. Correct answer: − . 171 kg · m / s. Explanation: Remember that magnitude refers only to the length of a vector, not its direction. So if louey (cal2859) – Ch1-H3 – florin – (56930) 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) × ( 48 , , ) m / s | = |( 2 . 736 , , ) kg · m / s | = 2 . 736 kg · m / s ....
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This note was uploaded on 03/20/2012 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas.
- Spring '08