Work is said to be one Joule when a force of
- A.4 N moves an object by 25 cm.
- B.2 N moves an object by 1 m.
- C.1 N moves an object by 1 cm.
- D.1 N moves an object by 50 cm.
Correct answer
Explanation
The correct answer is A, 4 N moves an object by 25 cm. Work equals force multiplied by displacement, and 4 N multiplied by 0.25 m gives exactly 1 joule.
One joule is the work done when a force of one newton moves an object through one metre in the direction of the force, so 1 J = 1 N m. Work is a scalar quantity, and it is done only when the object actually moves along the line of the force; pushing a wall that does not move does no work. Before multiplying, the displacement must be changed into metres: 25 cm is 0.25 m. The unit is named after James Prescott Joule, who showed that work and heat are forms of the same energy.
B is wrong because 2 N multiplied by 1 m gives 2 J. C is wrong because 1 N multiplied by 0.01 m gives only 0.01 J. D is wrong because 1 N multiplied by 0.5 m gives 0.5 J.
Exam tip: work (J) = force (N) multiplied by displacement (m); always change cm into m first.
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