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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