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Is this projectile motion?

  1. Nov 7, 2007 #1
    Is this projectile motion??

    1. The problem statement, all variables and given/known data

    A projectile is shot straight up from the earth's surface at a speed of 1.30×104 km/hr.

    How high does it go?



    Is this just a projectile motion problem? Or is it different because it has something to do with the theory of gravity??? (because that is the section we are on in class).
     
  2. jcsd
  3. Nov 7, 2007 #2
    Just a projectile motion problem.
     
  4. Nov 7, 2007 #3
    Oh, ok...

    Thanks
     
  5. Nov 7, 2007 #4

    Dick

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    I think you mean 1.30*10^4km/hr, but I could be wrong. If so then it is fast enough that you can't take g=constant. So it's a gravity problem. It might be handy to know something about conservation of energy.
     
  6. Nov 7, 2007 #5
    Oops.. Yes I do mean 1.30*10^4...
     
  7. Nov 7, 2007 #6

    Dick

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    Ok, then you just need to know an expression for gravitational potential energy that is more general than mgh.
     
  8. Nov 8, 2007 #7
    I think it's a free-fall motion problem. You use the UAM (uniformly accelerated motion) formula d = (Vf^2 - Vi^2) / 2g, but make sure that g is negative since the projectile was shot upwards.
     
  9. Nov 8, 2007 #8

    Dick

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    Wrong, the projectile is moving at nearly orbital velocity. You can't take 'g' constant.
     
  10. Nov 8, 2007 #9

    rl.bhat

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    Use conservation of energy principle.
    KE = 1/2.mv^2
    PE= GMm/(R + h). Substitute GM = gR^2. Find the value of h
     
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