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
Correct answer
Explanation
The correct answer is B, half of mass into the square of the speed. 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.
Option A is the expression for gravitational potential energy near the surface of the Earth, that is mass into acceleration due to gravity into height, and it depends on position rather than motion. Option C, mass into speed, is the linear momentum of the body, a vector quantity measured in kilogram metre per second, not an energy at all. Option D leaves out the factor of one half and is the standard careless error in this question. Remember also that kinetic energy can be written as the square of momentum divided by twice the mass.
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
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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 →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
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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.
Read the full explanation →The commercial unit of electrical energy is the
- A.Joule
- B.Watt
- C.Kilowatt hour
- D.Erg
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Household electricity is billed in these units, and one kilowatt hour, popularly called one unit, is the energy consumed when an appliance of one kilowatt runs for one hour; in SI terms it equals 3.6 million joule.
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