Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What formula can i use?

  1. Sep 14, 2008 #1
    what formula can i use when i wanted to find out the velocity of two moving object?

    like 2 car going foward on the same road but different speed. Car 1 in front is at 30m/s and car 2 in back is going 60m/s. how can i find the velocity of car b relative to car a?
  2. jcsd
  3. Sep 14, 2008 #2
    Let's say car A was moving at 30m/s and car B was also at moving at 30m/s, if they looked at each other they wouldn't be moving, so their relative velocity is 0.
    But if a car C was moving at 60m/s both car A and B would agree it was moving at 30m/s.

    So the formula is quite simple: relative V=V1-V2=60m/s-30m/s=30m/s.
    Also V2-V1 doesn't equal -30m/s, it only means I think you're going at 30m/s in the other direction.

    Always think of it as if the first variable was standing still.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook