Mar 6th 2013, 09:58 AM
Join Date: Jun 2010
Location: Naperville, IL USA
For #3 use the relationship Sum of Forces = ma. You found sum of forces already (you called it F_net), but what do those forces consist of? Theres' one force pushing on the box (196N) and another force resisting that movement. So F_friction = F_net - F_push. Then use the concept that F_friction = Normal force (i.e. weight) times coefficient of friction, and solve for the coefficient of friction.
For #4 the forces acting on the crate are the 60N push minus the force of friction, which is its normal force to the floor (it's weight in this case) times the coefficient of friction. Set his sum of forces equal to ma, and solve for a. Now yuo can determine distance and velocity using standard equations of motion, such as v=at and d = (1/2)at^2.