## Physics Technology Update (4th Edition)

Assume that the force of drag is proportional to velocity. This means that the net force is equal to weight minus drag, which would be $F=mg-kv$, where $k$ is a constant. The acceleration would be equal to $a=\frac{F}{m}=\frac{mg-kv}{m}=g-\frac{k}{m}v$. As mass increases, acceleration becomes larger and the drag force becomes less effective. Therefore, the time it takes for the Ball 1 to reach the ground will be less than the time for Ball 2.