Your younger brother is supposed to mow the lawn using a push mower. He reasons from the Newton's Third Law that the mower will push back with the same force he exerts on the mower; therefore nothing will move and attempting to mow the lawn is pointless. What is wrong with his reasoning? a: The boy has not enough push force on the mower b: the boy forgot friction force c: From the 3rd law, no force on mower, but mower has initial speed therefore the mower can keep moving d: The boy exerts a force on the mower, but the reaction force is exerted by the mower on the boy. The two forces are acting on different objects, and thus cannot cancel. The answer is D but I need to know why. From what I understand, two forces acting on different objects DO constitute a 3rd law pair. The boy on the mower and the mower on the boy. The thing thats propelling them forward is the force of the surface on the boy as he pushes back on the surface. The static friction force. From my reasoning the answer should be B.... I appreciate your help.