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: Initial Velocity with angles

  1. Jul 20, 2016 #1
    1. The problem statement, all variables and given/known data
    Disk P (inertia 0.41 kg ) moves at an unknown velocity across a low-friction horizontal surface and collides with disk Q (inertia 0.75 kg ), which is initially at rest. After the collision, the two (now slightly dented) disks move apart without spinning. Velocity information is provided in the initial and final top-view diagrams in the (Figure 1) .

    What was the initial velocity of disk P?
    What fraction of the initial kinetic energy is converted during the collision?

    2. Relevant equations
    v1im1 + v2im2 = v1fm1 + v2fm2

    3. The attempt at a solution
    So I know you use conservation of momentum, but I'm not entirely sure how to set up the equations to include theta.
  2. jcsd
  3. Jul 20, 2016 #2


    User Avatar
    Homework Helper
    Gold Member
    2017 Award

    Momentum is a vector quantity. So, the relevant equation is a vector equation

    m1 v1i + m2 v2i = m1 v1f + m2 v2f

    In terms of x components:

    m1 v1ix + m2 v2ix = m1 v1fx + m2 v2fx

    (There is a similar equation for the y components.)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted