SAT Subject Physics Practice Question 620: Answer and Explanation

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Question: 620

1. An electron is allowed to freely move between a pair of parallel plates that have a 1.5 volt potential difference. The electron starts at the negative plate. The velocity of the electron as it strikes the positive plate is most nearly

A. 7.3 × 10-8 m/s
B. 7.3 × 10-5 m/s
C. 7.3 × 105 m/s
D. 7.3 × 108 m/s
E. 7.3 × 1011 m/s

Correct Answer: C


The correct answer is (C). The voltage of the battery is equal to electrical potential energy, and the kinetic energy is .5mv2. Setting the two equal to each other, .5mv2 = (1.5V)(q). Solving the equation yields 7.3 × 105m/s, which is the velocity of the electron just as it reaches the positive plate of the battery.

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