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!

Homework Help: Momentum Question: Asteroid Collision

  1. May 8, 2013 #1
    1. The problem statement, all variables and given/known data

    Asteroid A is travelling at 40.0m/s and collides with asteroid B which is at rest. Both asteroids have the same mass, but asteroid A deflects off of its path by 30.0° above the horizontal, and asteroid B begins to travel 45.0° below the horizontal. What is the speed of asteroid A?

    2. Relevant equations

    PA1X = PA2X + PB2X

    PA1X = 40.0m/s*mA

    PA2X = mA*VA2*cos30°

    PB2X = mB*VB2*cos45°

    PA2Y = mA*VA2*sin30°

    PB2Y = mB*VB2*sin45°

    3. The attempt at a solution

    Equation #1 mB*VB2*sin45° = mA*VA2*sin30°
    Equation #2 mB*VB2*cos45° + mA*VA2*cos30° = 40.0m/s*mA

    I isolate mB*VB2 from Equation #1 and get mB*VB2 = (mA*VA2*sin30°)/(sin45).

    Now I substitute mB*VB2 into Equation #2, and get (cos45°*VA2*sin30°)/(sin45°) + VA2*cos30° = 40.0m/s, I cancelled out mA.

    Next I isolate VA2*(sin30°)/(tan45°) + cos30° = 40.0m/s

    Finally VA2 = 78.2679m/s which is impossible because it shouldn't go faster after the collision. Also, my textbook's answer is 23.3m/s.
  2. jcsd
  3. May 8, 2013 #2


    User Avatar

    Staff: Mentor

    Careful... didn't VA2 multiply both terms on the left?
    Yup, 78 m/s is definitely too large. It's also possible that your textbook's answer is not correct :wink:
  4. May 8, 2013 #3
    You're right - thank-you so much!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted