Question

Can work done by a body be negative or positive?

Answer 1

Work done:

1. When a force acts on an object, it causes it to move; work is said to have been done on it.
2. For work to be done, a force must be exerted, and there must be motion or displacement in the direction of the force.
3. The work done by a force acting on an object equals the magnitude of the force multiplied by the distance moved in the direction of the force. Work has only magnitude and no direction. Hence, work is a scalar quantity.
4. The work done by a force is defined as the product of the component of the force in the direction of the displacement and the magnitude.
5. Mathematically, it can be expressed as,

$\text{W = F d cos θ}$

Where,

$\mathrm{W}$ is the work done

$\mathrm{F}$ is the force

$\mathrm{d}$ is the displacement

$\mathrm{\theta }$ is the angle between force and displacement

$\mathrm{F}\mathrm{cos\theta }$ is the component of force in the direction of displacement.

Work done by a force applied on a body is:

1. The work done is positive if the direction of force and displacement are the same.
2. The work done is zero when force and displacement are perpendicular. If an object is not moving, then $\mathrm{d}=0$, so $\mathrm{W}=0$
3. If the object is moving in the opposite direction to the direction of the applied force, the work done is negative.