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Homework Help: Starship + 2 different planets?

  1. Sep 28, 2010 #1
    Starship + 2 different planets????

    1. The problem statement, all variables and given/known data
    The problem from my textbook is:
    Inside a starship at rest on earth, a ball rolls off the top of a horizontal table and lands a distance D from the foot of the table. This starship now lands on the unexplored Planet X. The commander, Captain Curious, rolls the same ball off the same table with the same initial speed as on earth and finds that it lands a distance 2.76D from the foot of the table. What is the acceleration due to gravity on Planet X?


    2. Relevant equations
    The 4 basic equations of motion:
    V=Vi + a x delta t
    S=Si + Vi x delta t + 1/2at^s
    S=Si + 1/2(V+Vi)delta t
    V^2= Vi^2 + 2a(S-Si)


    3. The attempt at a solution
    I know the initial velocity is the same in both cases, I figure you have to substitute the initial velocity in one with an equation with the acceleration on earth. I'm kind of lost from this point.
    What I really need is some one to explain how to solve it.
     
    Last edited: Sep 28, 2010
  2. jcsd
  3. Sep 28, 2010 #2

    kuruman

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    Re: Starship + 2 different planets????

    This is a projectile motion problem. You need to find an expression for the range of the projectile given that it has initial velocity v0 only in the horizontal direction and starts at height h above ground. Can you find such an expression?
     
  4. Sep 29, 2010 #3
    Re: Starship + 2 different planets????

    I'd have to rearrange equations and substitute them into one another and I wouldn't know where to start.
     
  5. Sep 29, 2010 #4

    kuruman

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    Re: Starship + 2 different planets????

    Start by writing expressions for the horizontal position of the ball at any time t and for the position of the ball above ground at any time t. Eliminate the time and find an expression giving the dependence of the range on the vertical height and the initial speed.
     
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