1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is this velocity right?

  1. Sep 14, 2008 #1
    Question: Look at figure 1.6. if Car a slowed to 30m/s. what would the velocity of car b relative to car a be?

    figure 1.6 is a picture of 2 car going forward the same way. Car a is in the front and car b is in the back. Car a is going at 40m/s and car b is going 60 m/s.

    will this be how i solve it?

    40m/s - 60m/s = -20 m/s

    is that how the answer is or i'm i wrong? is it another way?
     
  2. jcsd
  3. Sep 14, 2008 #2

    LowlyPion

    User Avatar
    Homework Helper

    But was that the actual question?
     
  4. Sep 14, 2008 #3
    yes that was the question.
     
  5. Sep 14, 2008 #4
    the problem is that i don't know if i solved it right.
     
  6. Sep 14, 2008 #5

    LowlyPion

    User Avatar
    Homework Helper

    Please read the problem more carefully.

     
  7. Sep 14, 2008 #6
    so the answer should be:

    30m/s - 60m/s = -30m/s

    ???? and thanks ;]
     
  8. Sep 14, 2008 #7

    LowlyPion

    User Avatar
    Homework Helper

    Not quite.

    Take the vector difference by subtracting the vector of car A from the vector of Car B.

    In the case where they were moving away the distance was getting bigger. Subtracting from the second really resulted in adding. In this case the vector of the second is larger and when you subtract the vector (of the one you want it relative to) it's not (-) it's (+). Reverse the order of the subtraction in the equation you gave.
     
  9. Sep 14, 2008 #8
    thanks so much ;]
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?