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!

Basic dynamics/acceleration question

  1. Apr 3, 2014 #1
    1. The problem statement, all variables and given/known data

    A 1000kg car is travelling at 27.0 m/s. Determine the force required to stop it in 70.0 m.


    3. The attempt at a solution

    I attempted to treat this question as if I knew how many seconds it took to stop, and did this:

    70.0m / 27.0m/s = 2.59259s

    2.59259s / 27.0m/s = 0.096

    1000kg / 0.096 = 10414.29N

    F = 10.4kN

    But then I realized that this is all predicated on the idea that we are moving at 27.0 m/s throughout the whole 70.0m rather than accelerating. Now I have no idea what to do, and both of my textbooks are proving useless. Please help, and sorry if the question is messed up or hard to decipher, this is my first post.
     
  2. jcsd
  3. Apr 3, 2014 #2

    PhanthomJay

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    You should first understand and become familiar with the SUVAT equations of motion for constant acceleration which you can find in any text to solve for the acceleration, then correctly apply Newton's Laws.
     
  4. Apr 4, 2014 #3

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    "suvat" equations are sometimes called "kinematic equations"
    you can also work stuff out from the velocity-time diagrams.

    you should have had some coursework about force and acceleration
    - if you have not seen v-t diagrams, then you have probably had some work on average velocity.

    Using average velocity to do this will make most people here cringe, but some courses do it that way at first.
     
  5. Apr 4, 2014 #4
    Ahh okay, yeah we've done kinematic equations, but I was having a hard time remembering them, and we never referred to SUVAT at all as an acronym. Thanks so much for the help guys, I finally got the right formula for the question:

    a = (Vf^2 - Vi^2)/2D

    F = 5.26kN

    Thanks for helping my (now seeming stupid) question!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Basic dynamics/acceleration question
Loading...