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Velocity correction #2

  1. Sep 14, 2008 #1
    Question: Look at figure 1.8. If car A were to increase its speed to 60m/s, what would be the velocity of car A relative to car B.

    figure 1.8 is a picture of two car going different direction basically facing each other. Car a on the right is going at 40m/s and car b on the left is going at 60m/s.

    60m/s - 60m/s = 0m/s

    is this right?

    Question #2: Two trains move on parallel tracks in opposite directions away from each other. one moves at the rate of 50m/s , while the other moves at 70m/s. what is the magnitude of the velocity of each train relative to the other?

    50m/s - 70m/s = -20m/s

    70m/s - 50m/s = 20m/s

    is this right?

    Thank You.
  2. jcsd
  3. Sep 14, 2008 #2


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    The first is right the second is not.

    If you were moving away from something not moving your relative velocity would be your speed in the direction you are going. But what happens if that stationary object moves on its own away from where you are going. Does that mean you are moving slower AWAY from the object or faster? What do the velocities do? Subtract or add?
  4. Sep 14, 2008 #3
    70m/s + 50m/s = 120m/s

    is this correct? and thanks for all the help.
  5. Sep 14, 2008 #4


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    There you go.
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