Question

Mark the correct statement(s) related to work.

• A. Work done by a force can be different as measured by different observers.
• B. Work done by a force can be zero even though the force in non zero.
• C. Work done by a force on a object would be non zero if the force is not perpendicular to displacement of object.
• D. None of the above

Answer 1

Answer: (A), (B), (C)

Work done by a force on a object would be non zero if the force is not perpendicular to displacement of object.

Correct options explanations:

Work done may be defined as the product between the force applied to the body, and the displacement caused due to the force, with the cosine of the angle between the force and displacement.

Let,

F = force

S= displacement ,

∅= angle between force and displacement

W (work done) = F x S Cos ∅

1. Option A: The work done by a force can vary depending on who is measuring it. For example, the person standing in the direction of the displacement, and the person standing in the direction opposite to the direction of displacement, would have different measures and reference points for force and displacement, and hence the work done calculated by each would be different.
2. Option B: Work done by a force can be zero even though the force is not zero. We know that work done (W) is calculated by the product of force, displacement caused, and the cosine of the angle between them (W = F x S Cos ∅). When the angle between the force and displacement is perpendicular to each other, the work done will be zero, as the cosine of 90° is zero.
3. Option C: Work done by a force on an object would be non-zero if the force is not perpendicular to the displacement of the object. We know that work done (W) is calculated by the product of force, displacement caused, and the cosine of the angle between them (W = F x S Cos ∅). When the angle between the force and displacement is not 90° (that is they are not perpendicular) then the value of work done will not be zero.

Hence, Option a, b, and c are correct.