If a force of 12 N acts on a car and changes its momentum from 36 kgm/sec to 60 kgm/sec, the time during which this change occurs will be
Correct answer: B. 2 sec
- A. 24 sec
- B. 2 sec
- C. 12 sec
- D. 8 sec
Explanation
To solve this problem, use the impulse-momentum theorem, which states that the impulse (force multiplied by time) is equal to the change in momentum. The formula is:F×t = mvf - mviSubstitute the given values: F = 12 N, mvf = 60 kgm/s, and mvi = 36 kgm/s.Therefore, t = (60 kgm/s - 36 kgm/s) / 12 N = 24 kgm/s / 12 N = 2 sec.This means the correct time interval is 2 seconds.Options 24 sec, 12 sec, and 8 sec are incorrect because they result from errors in dividing the change in momentum by the force.
This question appeared on the UHS MDCAT 2010 paper, which you can sit online with every answer explained.
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About Linear Momentum
Linear momentum is the vector product of mass and velocity, p = mv, and changes when a net external force acts. Work includes impulse as the change in momentum, conservation of momentum in isolated systems, collisions and explosions, and the distinction between elastic, inelastic and perfectly inelastic collisions.
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