Which one of the following is NOT the unit of energy?
- A.Joule
- B.Watt-hr
- C.Newton-metre
- D.kg-metre/sec²
Correct answer
Explanation
The correct answer is D, kg-metre/sec². A kilogram-metre per second squared is mass times acceleration, which is force; it is the newton, not a unit of energy.
Energy and work have the dimensions of force multiplied by distance. The SI unit of energy is the joule, defined as the work done when a force of one newton moves its point of application through one metre, so one joule equals one newton-metre, or one kg·m²/s². The watt-hour is the energy used when a power of one watt acts for one hour, equal to 3,600 joules; electricity bills use the kilowatt-hour, called one unit, equal to 3.6 × 106 joules. Other energy units include the calorie, the electron volt and the erg.
A is wrong because the joule is the SI unit of energy. B is wrong because the watt-hour is power multiplied by time, which is energy. C is wrong because the newton-metre, force multiplied by distance, is equal to the joule.
Exam tip: newton = kg·m/s² (force); joule = N·m = kg·m²/s² (energy); 1 kWh = 3.6 × 106 J.
Practice Questions
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- A.1,2 and 3
- B.2 and 4
- C.1 and 3 only
- D.1 only
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- A.Magnesium
- B.Zinc
- C.Aluminium
- D.Lead
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- A.half of its original value.
- B.double of its original value.
- C.one-fourth of its original value.
- D.four times of its original value.
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- A.Ernest Rutherford
- B.J.J. Thomson
- C.Niels Bohr
- D.Albert Einstein
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- A.B
- B.2B
- C.B/2
- D.B/4
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