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Review Q #4 (Motion in Two/Three Dimensions)

  1. Sep 21, 2010 #1
    1. The problem statement, all variables and given/known data
    The "Solar Sail I" experimental spacecraft is launched from the international space station with an initial velocity of 12 m/sec in a direction that makes a 120 angle with respect to the direction of radiation coming from the sun. Measurements show that an acceleration of 0.5 m/sec is imparted to the spacecraft by the pressure of sunlight pushing against its soar sail. Calculate the time taken for the spacecraft speed to increase 100 m/sec.

    2. Relevant equations
    Vx = VoCosAo
    Vy = VoSinAo - gt


    3. The attempt at a solution
    I don't get what direction the radiation is coming in, no idea where to start?
     
  2. jcsd
  3. Sep 21, 2010 #2

    ehild

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    Read the problem text again and make a figure.
     
  4. Sep 21, 2010 #3
    If I set the direction of the spacecraft along the x axis in the west direction, would that mean the angle is 30 degrees north of west which would result in a 120 degree angle for the sun?
     
  5. Sep 21, 2010 #4

    ehild

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    It looks OK.


    ehild
     
  6. Sep 21, 2010 #5
    I think I'm supposed to use the relative velocity formulas?
    bolded = vector
    VP|A=VP|B+VB|A ?

    This is probably the hardest one for me to comprehend :(
     
  7. Sep 21, 2010 #6

    ehild

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    I think that the velocity of the spacecraft is given with respect to the Space Station which is considered an inertia system. You have a specific direction: that of the Sun. The Sun is very far away so its rays can be considered parallel, as shown in the attachment. The motion of the spacecraft is like that of a projectile. I hope the problem was meant in this way but I may be wrong.

    ehild
     

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  8. Sep 21, 2010 #7
    That's the way I was picturing it.
    Is it similar to a plane flying in crosswind?
    That's the only thing I can think of :X which is in the relative velocity section.
    The example/figure/diagrams also look similar.
    I'm not too strong in the relative velocity section :(

    Can anyone give some more input on this? This is the last problem I need to understand :)
     
  9. Sep 21, 2010 #8

    ehild

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    Do not worry about relative velocity. You are given the initial velocity and the acceleration. The initial velocity has both horizontal and vertical (or westward and northward) components the acceleration is horizontal (westward)


    ehild
     
  10. Sep 21, 2010 #9
    So which angle would I use for the formulas?
    60 degrees ? or the entire 120 degrees?
     
  11. Sep 21, 2010 #10

    ehild

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    Do according to the picture. As you need the magnitude of the components, use 60 degree.
     
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