question_answer 40)

  Show that a force that does no work must be a velocity dependent force.

Answer:

                  Let a forcedoes no work for the displacement while moving with velocity  for time dt. Then work done, dW = or or or = 0 or = . Therefore, for no work done, must be velocity dependent if angle between  and  is 90°. If changes its direction, then should also change its direction so that angle between  and  is 90°. It is so when a charged particle is moving in a perpendicular uniform magnetic field.