Question

The minimum force required to cause motion of a certain body is 50N. Find a) the magnitude of frictional forcewhen the applied force is less than 50N. b) the part of a force of 60N that causes motion. c) the max. frictional force in this case.

Answer 1

Obviously, it is apparent that since altleast 50N is required to move the object, we can say that at that point limiting equilibrium exists, I. e, slightly higher force will overcome friction. So, the maximum value of friction is 50N(actually negligible lesser than 50).The magnitude of friction when applied force is lesser than 50 is equal to the magnitude of the force itself. If 60N is applied, friction applies 50N opposing it, but there is a net 10N which makes the object move. The max frictional force is 50N.