Homework Help: Physics

Posted by Mariah on Wednesday, March 7, 2012 at 11:20pm.

A projectile mass of 0.500 kg is shot straight up with an initial speed of 28.0 m/s.
A. How high would it go if there were no air friction?
I got this answer, it is 40 m.
B. If the projectile rises to a maximum height of only 34.0 m, determine the magnitude of the average force due to air resistance.
The correct answer is 0.865 N but I cannot figure out how to do it. Thanks!

Physics - drwls, Thursday, March 8, 2012 at 12:41am
B. The total energy is reduced by
deltaE = 6.0m*g*0.500kg = 29.4 joules at the top of the trajectory

The missing energy goes to doing work against friction, equal to F*34 m = 29.4 J

Therefore F = 29.4J/34m = 0.865 N

(assuming F is constant). If not constant, F is the average force
Physics - Mariah, Thursday, March 8, 2012 at 10:14am
Okay thank you!!

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