Name: Potential Energy of an Object at a Height
Uploaded: 2019-07-19
Duration: 8 min 3 s
Description: Gravitational potential energy is the energy stored in an object due to its position. It depends upon the height at which the object is placed. Let us derive...

Question

What is meant by work done by a force and work done against a force? Explain with suitable examples.

Accepted Answer

Work is said to be done when the body is displaced under the influence of an external force in the direction of the force.

Work done is given by the formula, $W = F \times s \times \cos θ$ where $F$ is the force, $s$ is the displacement and $θ$ is the angle between the direction of force and displacement.

When the body displaces in the direction of force, then $θ = 0 °$ and hence $\cos θ = \cos 0 ° = 1$ . So, when both force and displacement are in the same direction, the work done is positive. For, example, when we push a table, it moves in the direction of the push, then the work done by us is said to be positive.

When the body displaces in the direction opposite to that of force, then $θ = 180 °$ and hence $\cos θ = \cos 180 ° = - 1$ . So, when force and displacement are in the opposite direction, the work done is negative. For, example, when we push a heavy object, it moves a little. This is because the frictional force is acting on the object. In this case, the work done by the frictional force is negative as the direction of the frictional force is opposite to that of displacement of the object.

What is meant by work done by a force and work done against a force? Explain with suitable examples.

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