A 120-kg crate, starting from rest, is pulled across a floor with a constant horizontal force of 450 N. For the first 11 m the floor is frictionless, and for the next 11 m the coefficient of friction is 0.30. What is the final speed of the crate?

Question

A 120-kg crate, starting from rest, is pulled across a floor with a constant horizontal force of 450 N. For the first 11 m the floor is frictionless, and for the next 11 m  the coefficient of friction is 0.30.  What is the final speed of the crate?

drwls · Answer

Calculate the work done during each of the two periods (frictionless and with friction) and add them. Equate the Total Work sum to the final kinetic energy and solve for V. The M's will cancel out.