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Kinematics - marbles rolling down a ramp and into sand

  1. Mar 26, 2012 #1
    Kinematics -- marbles rolling down a ramp and into sand

    1. The problem statement, all variables and given/known data

    14) The student carries out an experiment to investigate momentum and collisions. A ball bearing is rolled down a ramp clamped at the edge of a bench. The ball bearing makes a head-on collision with a marble at the bottom of the ramp.

    The ball bearing and the marble both move forward in the initial direction of the ball bearing after the collision, landing in a tray containing a layer of sand.

    (a) Initially the ball bearing rolls down the ramp without the marble in a place. The ball bearing falls a verticle distance of 1.2m and lands a horizontal distance 95cm forward of the end of the ramp. Show that the speed of the ball bearing leaving the ramp is about 2ms-1
    I worked this out, CORRECTLY as 1.9 ms-1

    (b) When the ball bearing is rolled down the ramp with the marble in place, it knocks the marble forwards. The ball bearing lands a horizontal distance 64cm forward of the end of the ramp, and the marble lands a further 93cm forward from this position. Calculate the ratio of masses of the ball bearing and he marble

    ----------
    PART (b) IS THE QUESTION ON WHICH I AM STUCK


    2. Relevant equations
    v2 = u2 + 2as

    3. The attempt at a solution

    so

    m1u1 + m2u2 = m1v1 + m2v2

    m1u1 = 1.9m1
    m2u2 = 0

    1.9m1 = m1v1 + m2v2
    BUT I cannot find v1 OR v2 as I don't know the distance the balls FALL
     
  2. jcsd
  3. Mar 26, 2012 #2
    Re: Kinematics -- marbles rolling down a ramp and into sand

    isn't it 1.2 meters?
     
  4. Mar 26, 2012 #3
    Re: Kinematics -- marbles rolling down a ramp and into sand

    no that is the distance between the top and bottom of the ramp NOT the bottom of the ramp and the floor

    (imagine a ramp standing on a table - the 1.2 m deals with the height of the ramp)

    part (b) deals with the height above the ground - THERE MAY BE another way to do it but i figured my method was most logical!
     
  5. Mar 26, 2012 #4
    Re: Kinematics -- marbles rolling down a ramp and into sand

    oh so like this? and the ramp is 1.2 meters high from top to table?


    EDIT: actually now that I read this part more carefully: "The ball bearing falls a verticle distance of 1.2m"

    it seems to say that the 1.2 meters is the height from the tray to the bottom of the ramp
     

    Attached Files:

  6. Mar 26, 2012 #5
    Re: Kinematics -- marbles rolling down a ramp and into sand

    the diagram is exactly what is in the book and although it is unlabelled it would seem that the inital suggestion is correct :)
    (i.e: the BOOK diagram is unlabelled)
     
  7. Mar 26, 2012 #6

    gneill

    User Avatar

    Staff: Mentor

    Re: Kinematics -- marbles rolling down a ramp and into sand

    If you know the speed that the solo ball bearing left the ramp horizontally, and you know how far it traveled horizontally before it hit the sand, then surely you can work out the height of the drop from table to sand...
     
  8. Mar 26, 2012 #7
    Re: Kinematics -- marbles rolling down a ramp and into sand

    actually that cannot be correct because the ball will lose speed when it hits the marble :S
    if it helps the MS got an answer of 5.3 although I have no clue how :S
     
  9. Mar 26, 2012 #8
    Re: Kinematics -- marbles rolling down a ramp and into sand

    the height of the table is not going to change depending on if the ball is alone or if it is hitting a marble :)
     
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