How will you find the work done when a variable force acts on a body?

When a steady torque acts on a body it

What is the work done when the force on the object is zero?

Write an expression for the work done when a force is action on an object in the direction of its displacement?

Obtain graphically and mathematically work done by a variable force.

Under what condition a moving body will continue to be in the state of motion even when no unbalanced force acts on it?

What would be the work done when the displacement of the object is zero?

A rain drop of radius 2 mm falls from a height of 500 m above the ground. It falls with decreasing acceleration (due to viscous resistance of the air) until at half its original height, it attains its maximum (terminal) speed, and moves with uniform speed thereafter. What is the work done by the gravitational force on the drop in the first and second half of its journey? What is the work done by the resistive force in the entire journey if its speed on reaching the ground is 10 m s-^1 ?

A force of 7 N acts on an object. The displacement it, say 8m, in the direction of the force. Let us take it that the force acts on the object through the displacement. What is the work done in this case?

Give an example where work done by a force is zero.