Turn on thread page Beta
    • Thread Starter
    Offline

    2
    ReputationRep:
    Hi I'm really struggling with the question on momentum in 2 dimensions. I don't understand for example, this question:

    A rocket is moving at 8 ms-1. A meteroid travelling at 15ms-1 from behind at an angle of 45 crashes into the rocket and becomes embedded in it. The rocket has a mass of 350 kg and meteroid has mass of 20 kg. Work out velocity after collision.

    The method I've been using is working out the momentum parallel to rocket motion and adding to the rocket's momentum for the momentum before. I then work out the velocity by dividing by the two masses added togerher, but this doesn't give me the right answer? Where am I going wrong?

    THank you for any help
    Offline

    10
    I'll have to rush this answer as I don't have much time just now. I'm sure someone else will jump in.
    You need to apply conservation of momentum in both the y direction (direction of the rocket at the start - upwards, say, from bottom to top of page) and in the x direction. (Left to right)
    The rocket at the start has only momentum in the y direction. Let's say the meteor strikes it from behind coming from the left at 45 degrees.
    The meteor has momentum in both the y and x directions. (Two components)
    After the collision, the combined masses will have momentum in both x and y directions.
    What is true for this collision, is that the total momentum in the y direction before, is equal to the total momentum after. Similarly, total momentum in x direction before, is equal to total momentum after.
    Before in y direction: momentum of rocket plus y component of meteor.
    Before in x direction: x component of meteor.
    After collision: total momentum is still the same. (Vector sum)
    Offline

    10
    ReputationRep:
    draw a diagram
    and remember momentum is a vector and that the direction may make the momentum change negative or keep it positive.
    work out the horizontal and vertical componets of the vectors
    Offline

    2
    ReputationRep:
    A-multiply velocity by weight> B -add velocity together> and divide A BY B
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: January 16, 2010
The home of Results and Clearing

2,467

people online now

1,567,000

students helped last year

University open days

  1. Keele University
    General Open Day Undergraduate
    Sun, 19 Aug '18
  2. University of Melbourne
    Open Day Undergraduate
    Sun, 19 Aug '18
  3. Sheffield Hallam University
    City Campus Undergraduate
    Tue, 21 Aug '18
Poll
A-level students - how do you feel about your results?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.