A roller coaster car of mass 400kg starts from rest at point A and passes the point B with a speed of 3m/s . If the distance from point A to B is 20m, how long is the average friction force ?
I do not know the height difference h between a and b.
if it goes down a distance h the loss in potential energy = m g h
so
m g h = gain in kinetic energy + friction force F * 20 meters
400 * 9.81 * h = (1/2) *400 * 9 + 20 * F