SAT Subject Physics Practice Question 494: Answer and Explanation

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Question: 494

10. A 30 g icicle that is at a temperature 0°C falls 6 meters from the eaves of a house to the ground below. If 5% of the kinetic energy that the icicle possesses when it strikes the ground converts into heat, which of the following is plausible? (Note: Hfwater .335J/g).

A. The ice would become colder during the fall; therefore, no ice would melt.
B. This would not happen because it would break the law of conservation of mass.
C. Less than .3g of the icicle would melt.
D. The frictional work done to stop the icicle's fall would use up all the energy and leave none for anything else.
E. The icicle would shatter and the energy would convert into momentum.

Correct Answer: C


The correct answer is (C). The icicle strikes the ground with a velocity of 10.84 m/s, giving it a kinetic energy (1/2 mv2) of 1.76J. Only 5% of the energy is converted to heat, so the energy converted to heat is .088J. It takes .335 J to convert one gram of ice to water, so = .263g of ice is converted to water.

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