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Unformatted text preview: schopper (as55864) Ch1-HW3 Antoniewicz (56465) 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) 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. The two accelerations are about the same. 2. It is about half the acceleration of a falling rock. correct 3. It is about twice the acceleration of a falling rock. 4. It is much less than the acceleration of a falling rock. 5. It is much greater than the acceleration of a falling rock. 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 cars 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 = ( 52 , , ) m / s toward a wall. After bouncing off the wall, the tennis ball is observed to be traveling with velocity vectorv f = ( 43 , , ) 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 vectorp = ( vectorp x , , ) . Find 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: vectorp = vectorp f vectorp i = mvectorv f mvectorv i = m ( vectorv f vectorv i ) = m ( ( 43 , , ) m / s ( 52 , , ) m / s) = (0 . 057 kg) ( 95 , , ) m / s = ( 5 . 415 , , ) kg m / s . So 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 balls momentum? Answer in kg m / s. Correct answer: . 513 kg m / s. Explanation: Remember that magnitude refers only to the length of a vector, not its direction. So if schopper (as55864) Ch1-HW3 Antoniewicz (56465) 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) ( 52 , , ) m / s | = |( 2 . 964 , , ) kg m / s | = 2 . 964 kg m / s ....
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This note was uploaded on 09/12/2011 for the course PHY 303K taught by Professor Turner during the Fall '08 term at University of Texas at Austin.
- Fall '08