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# SAT Subject Physics Practice Question 194: Answer and Explanation

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Question: 194

 mass (in kg) speed (in m/s) Trial 1: 0.5 4 Trial 2: 1 3 Trial 3: 2 2 Trial 4: 3 1

40. The table records the mass and speed of an object traveling at constant velocity on a frictionless track, as performed by a student conducting a physics lab exercise. In her analysis, the student had to state the trial in which the object had the greatest momentum and the trial in which it had the greatest kinetic energy. Which of the following gives the correct answer?

Greatest Momentum      Greatest Kinetic Energy

A.   Trial 1        Trial 3
B.   Trial 2        Trial 2
C.   Trial 3        Trial 2
D.   Trial 3        Trial 3
E.   Trial 4        Trial 4

Since momentum, p, is equal to mv, we just multiply the two entries (m and v) in each row of the table and see which one is the greatest. This occurs in Trial 3, where p = (2 kg)(2 m/s) = 4 kg-m/s. So, the answer must be either C or D. To decide which, we only need to find the kinetic energy of the object in Trial 2 and Trial 3 and choose the one that’s greater. Since mv2 = (1 kg)(3 m/s)2 = J in Trial 2, but only (2 kg)(2 m/s)Previous       Next