According to the work-energy theorem, the work done by the net force on a body is equal to the change in its
- A.momentum
- B.kinetic energy
- C.potential energy
- D.power
Correct answer
Explanation
The correct answer is B, kinetic energy. The work-energy theorem states that the net work done on a body equals the difference between its final and initial kinetic energies, which is why a push that speeds a body up does positive work while friction, which slows it, does negative work.
Option A, momentum, changes with impulse, that is force multiplied by the time for which it acts, a different relation altogether. Option C, potential energy, changes with the work done against a conservative force such as gravity, and the theorem is not stated in those terms. Option D, power, is a rate and cannot be equated with work, which is a quantity. A useful check is that a force doing no work, such as the centripetal force, leaves the speed and therefore the kinetic energy unchanged.
Read the full article: Work, Energy and Power: Formulas, Units and Conversions
Practice Questions
View allWhat is the SI unit of work?
- A.Newton
- B.Joule
- C.Watt
- D.Pascal
Show answer
Work is the product of force and displacement, so its unit is the newton metre, which is given the name joule; one joule of work is done when a force of one newton moves a body through one metre in its own direction.
Read the full explanation →The work done by a force is zero when the angle between the force and the displacement is
- A.0 degrees
- B.45 degrees
- C.90 degrees
- D.180 degrees
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Work equals force into displacement into the cosine of the angle between them, and the cosine of ninety degrees is zero, so a force at right angles to the motion does no work at all.
Read the full explanation →The kinetic energy of a body of mass m moving with speed v is given by
- A.mass into g into height
- B.half of mass into the square of the speed
- C.mass into the speed
- D.mass into the square of the speed
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Kinetic energy is the energy a body has because of its motion, and it grows with the square of the speed, so a body moving twice as fast carries four times the kinetic energy.
Read the full explanation →What is the SI unit of power?
- A.Joule
- B.Watt
- C.Newton second
- D.Kilowatt hour
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Power is the rate of doing work, that is work divided by the time taken, so its unit is the joule per second, which is named the watt after James Watt.
Read the full explanation →One horsepower is approximately equal to
- A.100 watt
- B.500 watt
- C.746 watt
- D.1000 watt
Show answer
The horsepower is an older unit of power that survives in the rating of motors and vehicles, and one horsepower is taken as about 746 watt, that is roughly three quarters of a kilowatt.
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