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Homework Help: One seemingly easy problem. Please help due soon!

  1. Oct 31, 2009 #1
    One seemingly easy problem. Please help!! due soon!

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

    An astronaut of mass 77.0 kg is taking a space walk to work on the International Space Station. Because of a malfunction with the booster rockets on his spacesuit, he finds himself drifting away from the station with a constant speed of 0.660 m/s. With the booster rockets no longer working, the only way for him to return to the station is to throw the 9.65 kg wrench he is holding.
    In which direction should he throw the wrench?

    away from the station
    toward the station

    He throws the wrench with speed 14.82 m/s with respect to himself.
    After he throws the wrench, how fast is the astronaut drifting toward the space station?
    What is the speed of the wrench with respect to the space station?
    Your response differs from the correct answer by orders of magnitude.

    2. Relevant equations

    m1v1 = m2v2

    3. The attempt at a solution
    The astronaut obviously has to throw the wrench away from the station to be propelled back towards the station. I was also able to find number 2 using the formula above where m1 = mass of the astronaut + mass of the wrench. I am stuck on part 3. My intuition tells me that all I need to do to get this answer is to add 14.82 to the initial velocity of the astronaut but WebAssign will not take the answer. Please help. This is due in an hour and this is the only part of this hw that I am missing
  2. jcsd
  3. Oct 31, 2009 #2
    Re: One seemingly easy problem. Please help!! due soon!

    think to begin with that the are together making the equation
    (m1+m2) u =m1v1+m2v2
  4. Oct 31, 2009 #3
    Re: One seemingly easy problem. Please help!! due soon!

    There are 2 frames in your problem: one is space station and the other is astronaut holding wrench.

    In this problem, we assume that direction of motion is away from station. It means that velocity of wrench and astronaut holding wrench is positive and velocity of astronaut after throwing wrench is negative.

    From problem, we have speed of astronaut+wrench is 0.66m/s (respect to Station => v_SA = 0.66m/s). After throwing, speed of wrench respect to astronaut is 14.82 m/s ( v_AW = 14.82 m/s). To find speed of wrench respect to station, you just plus these 2 speeds: v_SW = v_AW + v_SA.

    You may remember that the sign of velocity is depend on its direction respect to your frame.
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