Applying Newton's Three Laws

When exactly enough force is applied for the block to move, the static frictional force will be equal to its maximum possible value. Thus:

Because the block rests on a horizontal plane, the normal force is simply equal to the weight of the block: F _N = 50N . Thus F _s = (50)(.75) = 37.5N . Recall that the static frictional force always cancels exactly with the force applied to the block. Thus the minimum necessary force to move the block is simply 37.5N .