MCAT Physics Question — Model Trains
 by
 Sep 29, 2017
 MCAT Question of the Day
Two model trains are propelled along a straight, frictionless track by electric motors. Train X has a total mass of 100g and is moving at speed v. Train Y has a total mass of 10g and is moving at speed 3v. The ratio of the kinetic energies of Train X to Train Y is:
A. 10:9
B. 9:10
C. 10:3
D. 1:9
Click for Explanation
The kinetic energy equation is Ekinetic = ½ mv2. We can plug in the values given and set up a ratio to answer the question.
E_{X} = ½ (100)(v)^{2}
E_{Y} = ½ (10)(3v)^{2} = ½ (10)(9v^{2})
E_{X} / E_{Y} = ½ (100)(v)^{2} / ½ (10)9v^{2}
E_{X} / E_{Y} = (100)(v)^{2} / (10)9v^{2}
E^{X} / E^{Y} = (10)(v)^{2} / 9v^{2}
E_{X} / E_{Y} = 10 / 9
Thus choice (A), 10:9 is the correct answer.
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