1. The problem statement, all variables and given/known data The mass of A is 5kg and the mass of B is 10kg. If the acceleration of A is 2m/s^2 which is smaller than acceleration of B, where A is placed on top of B, then the value of frictional force applied by B on A is: A) 50N. B) 20N. C) 10N. D) None of these 2. Relevant equations a(max)=meu*g frictional force=meu*normal force 3. The attempt at a solution normal force= 5*10=50N meu= 2/10 = 1/5 frictional force= 10N But I had to assume that 2m/s^2 was the maximum acceleration. Can I do that? Because otherwise there are too many unknowns. Thanks in advance!