Working out some simple physics and I can't figure out how to convert velocity to newtons for force.. A six pound (2.72kg) tonka truck is moving across a cardboard bridge at a constant velocity of .067m/s (estimated). I tried looking for a while but was unable to find the kinetic friction of plastic wheels on cardboard. Using newton's second law, I was able to make this equation: F-Fk=ma, so F = ma+Fk. Fk is muK*Fn, so the final equation is: F=ma+muK*fn. Because there is no movement in the Y direction, fn would be the weight, and in this case 26.7n. there is no acceleration, so would ma equal zero? Is there any way to find the kinetic friction between plastic and cardboard? Thanks guys!