Work done by magnetic force is zero. Explain.

Force acting on a particle is (2hati+3hatj) N. Work done by this force is zero ,when a particle is moved on the line 3y+kx=5 . Here value of k is

Statement I: Work done by constant force is equal to magnitude of force multiplied by displacement . Statement II: Work done is scalar quantity. It may be positive, negative or zero.

The electric potential at point A is 20 V and at B is -40v . Work done by an external force in moving an electron slowly from B to A.

Statement I: In a circular motion, work done by centripetal force is not always zero. Statement II: If speed of the particle increases or decreases in circular motion, net force, acting on the particle is not direction towards the centre.

Statement I: if work done by conservative force is negative then potential energy associated with that force should increase. Statement II: This is from the reaction Delta u =- W. Here Delta u is change in potential energy and W is work done by conservative force.

Statement I: Work done by normal contact force can be non -zero Statement II: Normal contact force is always perpendicular to displacement of object. (Here displacement is measured with respect to frame of reference attached to the two surface in contact. )

Work done becomes zero

State the conditions under which the work done by a force is positive or negative.