physics
posted by pat .
1) Two boxes are placed are placed side by side on a frictionless surface so that they touch each other. Box A has a mass of 4 kg. Box B has a mass of 12 kg. A constant force of 24 N is applied to box A. What force does box A exert on box B?

Box A exerts onto force b its acceleration as a force;
So F=ma
where 24=(12+4)a Then solve for a
a=1.5
Then the force that box a exerts on box b is
F=ma
=12*1.5
=18N 
Good work.