1. Limited time only! Sign up for a free 30min personal 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!

What should be the formula to solve this?

  1. Sep 7, 2011 #1
    This is the given problem:

    Cars A and B approach each other on a straight road from points 457 m apart. A has an initial velocity of 20 m/s and is decelarating at the rate of 0.4 m/s². B has an initial velocity of 5 m/s and is accelerating at the rate of 0.3 m/s². When will the cars meet and how far will car A have travelled?

    note: this is not homework guys. I just want to recall my physics. Thanks in advance.
     
  2. jcsd
  3. Sep 7, 2011 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Last edited by a moderator: Apr 26, 2017
  4. Sep 7, 2011 #3
    1. The problem statement, all variables and given/known data

    Cars A and B approach each other on a straight road from points 457 m apart. A has an initial velocity of 20 m/s and is decelarating at the rate of 0.4 m/s². B has an initial velocity of 5 m/s and is accelerating at the rate of 0.3 m/s². When will the cars meet and how far will car A have travelled?

    2. Relevant equations

    none

    3. The attempt at a solution[/b

    The formula I do know for the problem is
    Da + Db = 457
    Da = Vit + at²
    2

    and..

    Db= Vit + at²
    2

    is this right? if it is, then what is the next step to solve this? thanks in advance.
     
  5. Sep 7, 2011 #4
    Uniform Acceleration:

    vave=(vi+vf)/2

    is this the formula i should use? if it is. Can you explain to me how to solve this kind of problem? I only just need a guide not the exact answer.
     
  6. Sep 7, 2011 #5

    gneill

    User Avatar

    Staff: Mentor

    The first thing to do in these sorts of problems is to choose a coordinate system, then taking that coordinate system into account, assign values to all the constants in your equations of motion for the two bodies. Be careful with the signs of the values! They should correspond to what is happening in the coordinate system (The prose description can be a bit lax on specifying the signs that should be assigned to values, expecting the reader to sort it out by context).

    Use the 'complete' version of the equation of motion for constant acceleration for both bodies:
    [tex]x = x_o + v_o t + \frac{1}{2}a t^2 [/tex]

    What values will you assign to the constants for each body?
     
  7. Sep 7, 2011 #6

    Doc Al

    User Avatar

    Staff: Mentor

    I'd use the formula for displacement & time:
    [tex]x = x_0 + v_0 t + (1/2) a t^2[/tex]
    Hints: Let x0 = 0 for car A, thus x0 = 457 for car B.
    If car A's initial velocity v0 is +20 m/s, what would car B's initial velocity be?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: What should be the formula to solve this?
  1. What is this formula? (Replies: 1)

  2. What should be squared? (Replies: 11)

Loading...