Question

The air exerts a forward force of `10` `N` on the propeller of a `.20`-`kg` model airplane. If the plane accelerates forward at `2.0` `m``/``s^2`, what is the magnitude of the resistive force exerted by the air on the airplane?

Answer 1

9.6N

Explanation:

Using newtons second law
Fnet=ma
What is the net force of the plane? It is primarily forward but encounters some air resistance. So first, draw your free body diagram.

In our case, the magnitude of the thrust force is greater than the drag, so our Net force would be Thrust - Drag.

Note* For convenience, I will use Fd as drag force and P as thrust force.
Fnet=ma
`P-Fd=ma`
`10-Fd=(0.20kg)(2.0m`/`s^2`)
`10-Fd=0.4N`
`-Fd=-9.6`
`Fd=9.6N`