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: Elastic and Inelastic Momentum Problem

  1. Nov 19, 2015 #1
    1. The problem statement, all variables and given/known data
    A car whose mass is 2000 kg moves with a velocity of 30 m/s. It hits a stationary car that has the same mass. (Ignore all horizontal forces except for the ones that two cars exert on each other.)

    a) The two cars stick to each other after the collision. What is their velocity after the collision?

    b) In a different collision, with the same start, the cars do not stick to each other. After the collision the car that was originally at rest is observed to move with a velocity of 10 m/s at an angle of 35 degrees with the original motion of the other car. Find the momentum and velocity after the collision of the car that was originally moving.

    2. Relevant equations

    m2v2final + m1v1final = m2v2i + m1v1i

    3. The attempt at a solution
    for a) 2000v2+2000v1 = 2000(0) + 2000(30)
    and since they stick together we can consider them one mass
    4000Vf = 60000
    vf = 15 m/s

    for b) I don't know how to start because of the angle and it's inelastic because the cars do not stick together, right?

    my attempt (but probably very wrong):

    V2f - V1f = -(V2i - V1i)

    10 - V1f = 30

    V1f = -20 m/s ---> final answer for velocity

    p = m x v

    2000 kg x -20 m/s = 40000 kg m/s ----> final answer for momentum

    I don't know where the angle comes into play.....
  2. jcsd
  3. Nov 19, 2015 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Remember that momentum and velocity are vectors. That's where the angle comes in: Divide things into components.

    You might want to read this: Elastic and Inelastic Collisions
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted