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Please help with this gravity problem

  1. Feb 19, 2009 #1
    I really have no idea where to start or how to even do this...

    (a) What is the apparent weight of a 78-kg astronaut 5200 km from the center of the Earth's Moon in a space vehicle moving at constant velocity?
    (b) is this towards or away from the moon?
    (c) What is the magnitude of the apparent weight of a 78 kg astronaut 5200 km from the center of the Earth's Moon in a space vehicle accelerating toward the moon at 3.2 m/s^2?
    (d) is this towards or away from the moon?
     
  2. jcsd
  3. Feb 20, 2009 #2

    tiny-tim

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    Welcome to PF!

    Hi jfahlgr1! Welcome to PF! :smile:

    I don't really understand question (a) … is that the whole question? :confused:

    Let's go straight to question (c) …

    the apparent weight is the force exerted by the astronaut's feet and the spaceship on each other …

    calculate it using Newton's second law of motion, and the law of gravitational force. :smile:
     
  4. Feb 26, 2009 #3
    First of all you have to know the mass of the Moon first before getting the weight of the astronaut. You use this formula to find Fg:

    Fg = [tex]\frac{GM}{r^2}[/tex]

    where:
    G = gravitational constant (6.67 * 10-11)
    M = Mass of the Moon
    r = 5,200,000 meters (5200 km)

    After you get Fg then you mutiply it from the mass of the astronaut to get its weight.

    The direction in question D is is towards the moon because you already said that the vehicle is accelerating towards the moon at 3.2 m/s2.
     
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