What is the Magnitude of Average Force Due to Air Resistance?

[IShouldBSurfing]

Hello ! Wow, you guys are awesome, Thanks for all the help ! I've got another one I'm stuck on - ... I got part A.. the answer is 42.9082, but I can't get part B... ? help pleaaseee? thaaanks

A projectile of mass 1.100 kg is shot straight up with an initial speed of 29.0 m/s.
(a) How high would it go if there were no air friction?
m
(b) If the projectile rises to a maximum height of only 35.2 m, determine the magnitude of the average force due to air resistance.
N

 

[T@P]

Use the second law of Newton: You would have -mg - Fr = ma

similarly, by the kinematic equations, you can find aceleration by using a system of equations: v = v0 + at and x = x0 + v0t + (1/2)at^2

in the first, v is o since at the top the velocity is o, you really have two equations with two uknownsl; t and a.

once you have "a" you can use -mg - Fr = ma or Fr = mg-ma

Hope i was some help here. (tell me if i did something wrong, i make mistakes sometimes)

 

[IShouldBSurfing]

hm.. i didn't really understand what u said at all.. how am i supposed to find a when i don't know t ? ah, confused

 

[T@P]

its a system of equations that gets you t and a. The systems are
-29 = at
35.2 = 29t + (1/2)at^2
these two help you solve for a AND t (not that you need t)
does that help?