a crate mass 20 kg is being pushed by a person with horizontal force of 63 N, moving with a constant velocity [E]. find the force of kinetic friction.

Answer 1

Force friction is 63 N. Since the velocity is constant, there is no acceleration, and no force trying to prevent the crate from moving.
F is given as F = ma.
F is the net force: Fa (force applied) - Ff (force friction). If there is no acceleration, 'a' becomes zero, causing mass to cancel out as well, leaving you with F = 0, which means there is no change in the forces acting on the crate.