HW #1-3-solutions

# HW #1-3-solutions - pasha(sep635 HW#1-3 Antoniewicz(56445...

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pasha (sep635) – HW #1-3 – Antoniewicz – (56445) 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 - 0 5 s - 0 = 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 about twice the acceleration of a falling rock. 2. It is much less than the acceleration of a falling rock. 3. The acceleration of a falling rock increases as it falls, so the question is not meaningful. 4. The two accelerations are about the same. 5. It is about half the acceleration of a falling rock. correct 6. It is much greater than the acceleration of a falling rock. 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 v i = 51 , 0 , 0 m / s toward a wall. After bouncing o ff the wall, the tennis ball is observed to be traveling with velocity v f = - 46 , 0 , 0 m / s . v i v 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 p = Δ p x , 0 , 0 . Find Δ p x . Answer in kg · m / s. Correct answer: - 5 . 529 kg · m / s. Explanation: To find the change in momentum, we pro- ceed as follows: Δ p = p f - p i = m v f - m v i = m ( v f - v i ) = m ( - 46 , 0 , 0 m / s - 51 , 0 , 0 m / s) = (0 . 057 kg) × - 97 , 0 , 0 m / s = - 5 . 529 , 0 , 0 kg · m / s . So Δ p x = - 5 . 529 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: - 0 . 285 kg · m / s. Explanation: Remember that magnitude refers only to the length of a vector, not its direction. So if

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pasha (sep635) – HW #1-3 – Antoniewicz – (56445) 2 we want the change in magnitude, we need to take the magnitudes of p i and p 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 p i , | p i | = | (0 . 057 kg) × 51 , 0 , 0 m / s | = | 2 . 907 , 0 , 0 kg · m / s | = 2 . 907 kg · m / s . And for p f , p f = | (0 . 057 kg) × - 46 , 0 , 0 m / s | = | - 2 . 622 , 0 , 0 kg · m / s | = 2 . 622 kg · m / s . So the change in magnitude is p f - | p i | = - 0 . 285 kg · m / s . 005 (part 1 of 3) 4.0 points The “red planet,” Mars, has a mass of 6 . 4 × 10 23 kg and travels in a nearly circular orbit around the Sun, as shown in the following figure. x z Sun A B C D v A v B When Mars is at location A , its velocity is v A = 0 , 0 , - 35000 m / s . When it reaches location B , the planet’s ve- locity is v B = - 35000 , 0 , 0 m / s .
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