Posted by Nate on .
A rock is dropped. How fast will the 5.0 kg rock be traveling in 4.0s if a 5.o N force of air resistance acts on it?

physics 
drwls,
In the real world, the air resistance will not be constant as it falls. It will be proportiuonal to the square of velocity.
Assume that 5 N is the AVERAGE friction force during the 4 seconds. There is also a weight force of M g = 49 N pushing it down. The net average force in the downward direction is 44 N.
Impulse = 44 N * 4s = Momentum gain
= M*Vfinal
Vfinal = 44*4 /M = 35.2 m/s
Without friction, Vfinal would be
g*t = 9.8 * 4 = 39.2 m/s