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 when objects stick

  1. Apr 30, 2007 #1
    1. The problem statement, all variables and given/known data

    A trolley of mass 2kg, travelling at 3m/s, collides with a stationary 1kg trolley. If the trolleys stick together, calculate:
    a) the total momentum before thecollision
    b) the speed of the two trolleys arter th collision

    2. Relevant equations

    momentum = mass x velocity
    momentum before collision or explosion = momentum after collision or explosion

    a collision is where equal forces act in opposite directions. An explosion is when objects
    3. The attempt at a solution


    how do i get B?
     
  2. jcsd
  3. Apr 30, 2007 #2
    You get part b using the second equation.

    Total momentum before collsion=total momentum after collision.

    The fact that the cart sticks tells you what about their velocities after they collide?
     
  4. May 1, 2007 #3
    if they collide and stick dont you add there masses to together so you have


    2 x 3 = 2+1 x v

    6 = 3 x v

    6 / 3 = 2m/s

    is that right?
     
  5. May 4, 2007 #4
    is the answer the right units as well? I presume the direction is always written as positive in the outcome?
     
  6. May 4, 2007 #5

    Doc Al

    User Avatar

    Staff: Mentor

    Yes, your answer is correct in magnitude and units. But direction is irrelevant--all they ask for is the speed, which is always a postive number (or zero!).
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook