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Homework Help: A projectile of mass 1.100 kg is shot straight up with an initial speed of 29.0 m/s.

  1. Oct 24, 2004 #1
    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
     
  2. jcsd
  3. Oct 24, 2004 #2

    T@P

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    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)
     
  4. Oct 24, 2004 #3
    hm.. i didn't really understand what u said at all.. how am i supposed to find a when i dont know t ? ah, confused
     
  5. Oct 24, 2004 #4

    T@P

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    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?
     
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