1. Not finding help here? Sign up for a free 30min 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!

Linear Collisions; Conservation Law

  1. Sep 22, 2012 #1
    Hello Physics Forums!

    1. The problem statement, all variables and given/known data
    The student sets up a collision experiment with two masses on a horizontal air track, with two springs on each end. The mass of A is 100 g and B is 200 g. Each spring has a constant of 20 N/m. Spring 1 (left side) was initially compressed 5 cm
    to start mass A moving.

    a. Determine the speed of mass A as it leaves spring 1 [0.71 m/s]
    b. If A has a velocity of 20 cm/s to the right after it collides with B, determine the velocity of mass B. [0.25 m/s right]
    c. Determine the maximum compression of spring 2 when mass B collides with it. [2.5cm]

    2. Relevant equations
    Ep = 1/2kx2
    p = mv

    3. The attempt at a solution
    I solved part a readily using the conservation of energy law (Ep = Ek). When I tried to solve part b using conservation of momentum, however, I obtained an incorrect answer:

    Total momentum before = Total momentum after
    m1v1+m2v2=m1v3+m2v4
    (m1v1+m2v2-m1v3)/m2=v4
    [(0.1kg)(0.71m/s)+(0.2kg)(0)-(0.1kg)(0.02m/s)]/(0.2kg)= v4
    v4 = 0.35 m/s right

    Am I reading the question wrong? Are my formulae incorrect?​
     
    Last edited: Sep 22, 2012
  2. jcsd
  3. Sep 22, 2012 #2
    20 cm/s would be 0.20 m/s, not 0.02 m/s
     
  4. Sep 22, 2012 #3
    Hahahaha thanks for your help; I'll have to be more diligent with unit conversions next time!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook