A boy is pushing on a 64 kg box with 128 N of force. The box has a coefficient of static friction of 0.38 and a coefficient of kinetic friction of 0.26. The box does not move? a) Currently how much is the force of friction on the box?

b) What is the minimum force the the boy need to exert on the box to get it to start moving?

c) Suppose the boy now pushes on the box with the same force of what you calculated in part (b) above and the box begins to slide. Calculate the force of friction on the box after it starts to slide.

d) Explain why the force of friction changed .