A student pushes a stationary trolley to the right. The student says that the trolley pushes back with an equal force, so the two forces cancel on the trolley. Which correction is needed?
The backward force acts on the trolley, so the forces act on the same object.
The backward force acts on the student, so it must be smaller than the forward force.
The backward force acts on the trolley, so it must be smaller than the forward force.
The backward force acts on the student, so the forces act on different objects.