(i) Statement:

Algebraic sum of all the works done on a body is equal to change in the kinetic energy of the body.

$\therefore \Sigma W=\Delta K.E.$

(ii) Different works:

• By gravity = mgh

    h→vertical displacement.

• By friction = -F×s

    F→frictional force

    s→displacement along the frictional force.

    * work done by frictional force is always negative.

• By spring = $\frac{1}{2}kx^2$

    k→spring constant

    x→deflection of spring w.r.t. free length.

    * work is positive if it moves the body and negative if it opposes the motion of the body.