text: First, calculate the force due to friction, F_f = uN, where u is the coefficient of kinetic friction and N is the normal force on the crate, which is equal to its weight.  In this case, N = mg, so F_f = umg.  The resultant force, F, on the crate will be the applied force, P = 49 N, less the force of friction.  So F = P - F_f = P - umg.  The acceleration is found by using the formula F = ma, or a = F/m, where we were given the mass m and we calculated the resultant force F.