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Question

A mass of 10kg is at a point A on a table. It is moved to a point B. If the line joining A and B is horizontal, what is the work done on the object by the gravitational force? Explain your solution


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Solution

Diagram:

Explanation:

  1. The force is acting downwards in this case.
  2. Which is equal to the mass of an object multiplied by the acceleration due to gravity. F=mg=10×9.81=98.1N
  3. But, according to the question, displacement from A to B is horizontal.
  4. Then the angle made between force and displacement will be exactly 90°.
  5. As force and displacement are making a right angle with each other.
  6. Work done is the dot product of force and displacement.
  7. Now work done W= FScosθ, where F=Force, S=Displacement, Hence W=F×S×cos90°=0, As cos90°=0, whatever be the values of force and displacement,
  8. Thus, the net work done will be equal to zero. or W=0.

Therefore, the work done on the body by gravity is zero.


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