Posted by Nate on Thursday, December 16, 2010 at 9:04pm.
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, Friday, December 17, 2010 at 2:47am
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
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