Stuck on this problem

1. Sep 22, 2004

shawonna23

A rock of mass 33 kg accidentally breaks loose from the edge of a cliff and falls straight down. The magnitude of the air resistance that opposes its downward motion is 239 N. What is the magnitude of the acceleration of the rock?

I tried a=239*33 and I got 7.24 but that was wrong. Please help. I don't know what else to do.

2. Sep 22, 2004

Pyrrhus

What are the forces acting on the block?

What does newton's 2nd law state?

3. Sep 22, 2004

faust9

Did you draw a free body diagram of the falling rock including all forces acting upon the rock?

Did you write out $\sum \vec F=m\vec a$? I'm sure if you do the above and sum the forces you'll get the correct answer.