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: Find the initial velocity of truck before collision

  1. Mar 4, 2015 #1
    Question: A car of mass 1500kg collides head-on with a truck of mass 9000kg. After the collision, the wreckage is at rest. The speed of the car just before the collision was 30m/s. What was the speed of the truck just before the collision?

    Relevant Equation(s):

    m1v1+m2v2 = m1v1'+m2v2' (?)

    My Attempt:

    (1500kg)(30m/s)+(9000kg)( ___m/s) = (1500kg)(0m/s)+(9000kg)( 0m/s)
    (1500kg)(30m/s)+(9000kg)( ___m/s) = 0
    (45000 kg*m/s)+(9000kg)(___m/s) = 0

    Problem: It's 1 in the morning and I'm not understanding what I'm doing wrong. Am I using the right equation? Do I need to set up west and east on the x-axis??
  2. jcsd
  3. Mar 4, 2015 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member
    2017 Award

    Why do you think you are doing something wrong? You will get a negative answer, but that only tells you the truck is moving in the opposite direction of the car.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted