Question

what do you know by positive negative and zero work

Answer 1

If the direction of work done and direction of force is same then the work done is known to be positive. If force and work have opposite direction, work done is negative.
If there is no displacement of the object when force is applied, the work is zero.
:)

Answer 2

$\huge\underline\mathfrak{Positive\:Work:-}$

Work done is positive when a force acts in the direction of motion of a body.

Example :- A child pulls a toy car with a string horizontally on the ground.

Here work is positive

F * S

$\huge\underline\mathfrak{Negative\:Work:-}$

Work done is negative when a force acts opposite to the direction of motion of the body.

Example:- When we kick a football lying on the ground, the force of our kick moves the football . When the direction of force applied and motion of football is same so work done is positive.

But when the football shows due to force of friction acting in a direction opposite to the direction of motion of football, thus work done is negative.

$\huge\underline\mathfrak{Zero\:Work:-}$

Work done is zero when a force acts at right angles to the direction of motion.

Example:- The moon moves around the earth in circular path. Here force of friction acts on the moon at right angles to the direction of motion of the moon. So work done is zero.

• (-) sign includes that work is done against the gravity.