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Launching from Mars

  1. Oct 25, 2008 #1
    1. The problem statement, all variables and given/known data
    The Radius of Mars is R_m
    its mass is m

    The radius of Mars (from the center to just above the atmosphere) is R_m and its mass is m. An object is launched from just above the atmosphere of mars.

    A) what is the object's initial velocity if its final velocity is V_f

    2. Relevant equations

    a=(v^2)/R <--wat v is this?

    3. The attempt at a solution

    i dont know how to start

    im thinking i need to calculate the gravity from mars?
    but if all im given is mass and radius
    how do i calculate it?

    i need to find the amount of work done by mars right?
    Last edited: Oct 25, 2008
  2. jcsd
  3. Oct 25, 2008 #2
    I think you need to use Newtons universal gravity law....


    This means that the force is equal to the constant G (6.67X10^-11) multiped by both masses, all of this divided by the distance between them squared.

    this will get you the Force.

    So now you have force, you know that Fnet=ma, so the acceleration will be {(Gm1m2)/R^2}/m

    finally, Vf^2-Vo^2=2a(x), so you simply solve using the above equation as a, and they just say to use Vo i believe
    I dont think this is a problem you shoudl get numbers for, it seems like a concept that you just want to work through with different equations and not really use numbers.

    This is just from what I understand.

    Good luck!
  4. Oct 26, 2008 #3
    im solving for Vo

    the object is launched from above the atmosphere

    im given the distance between object and mars (R_m)
    and I'm given the weight of mars (m)

    and I'm given Vf of the object

    so what I did (but I did not get a good answer)

    was use


    m1 = object
    m2 = mars
    r=distance from mars and object

    so the F equals

    F= Gm1m2/(R_m)^2

    and then I think I'm suppose this formua

    total W = deltaKE

    F*d = .5m1vf^2 - .5m1vo^2

    but how do I find d?

    I think this is right

    how do I use

    vf^2-vo^2 = 2a (x) <--whats x ?
  5. Oct 26, 2008 #4
    With what you have you won't be able to find work and finding energy is also not going to work out. I can't help if you dont supply numbers, I solved it simply with the units, plugging the numbers in should have yielded the answer.

    From what I can understand by your explanation that is anyway, it doesn't seem like work is in anyway involved.
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