Two objects, P and Q have the same momentum. Q has more kinetic energy than P if it:
Correct answer: B. Is moving faster than P
- A. Weighs more than P
- B. Is moving faster than P
- C. Weighs the same as P
- D. Is moving slower than P
Explanation
To determine which object has more kinetic energy when two objects have the same momentum, examine their speeds. Momentum (p = mv) being equal means that a heavier object (Q) must be moving slower than a lighter object (P) to maintain the same momentum. However, kinetic energy (KE = (1/2)mv2) is more affected by speed than mass because velocity is squared in the formula. Therefore, if Q is moving faster, it will have more kinetic energy despite potentially having less mass. This makes option B correct. Options A and D are incorrect because they imply Q is moving slower, which would result in less kinetic energy. Option C is incorrect because the same mass and momentum imply the same speed and kinetic energy.
This question appeared on the ETEA MDCAT 2016 paper, which you can sit online with every answer explained.
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About Kinetic Energy
Kinetic energy is the energy of motion, given for a nonrelativistic object by K = ½mv², so it depends on mass and the square of speed. Questions connect kinetic energy with work through the work energy theorem, calculate changes in kinetic energy, and distinguish it from momentum and potential energy.
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