Answer to Question #138711 in Physics for Briana

Question

Question 3: An airplane coming in for a landing is experiencing a force from its engines of 1800 N in the positive direction,
and a force from air resistance of 3200 N in the negative direction. If its acceleration is -0.3 m/s? what is the
mass of the plane?

Question 4: This is a conceptual short answer question. Explain your reasoning in full sentences.
Newton's 3rd Law says that if you pull a wagon forward, the wagon pulls you backward with an equal amount of
force. If this is true, how is it possible for you to make the wagon move? Specifically, explain how you could
cause the wagon to accelerate, despite the force of you pulling the wagon forward being equal to the force of the wagon pulling you backwards.

Answer 1

3)

$$F-F_{air}=ma\\1800-3200=-0.3m\\m=46667\ kg$$

4) The force that you exert on the wagon will cause it to move forward if it is greater than all opposing forces on the wagon. That is, the wagon will accelerate if the net force on the wagon is not zero. This is a proper application of Newton’s second law, but you cannot apply Newton’s third law in this case. Newton’s third law does not apply to the forces on a single object, but only to forces acting on two different objects. A Newton’s third law pair of forces can never cancel because they are always acting on different (opposite) objects.