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: Kinetic Energy Question

  1. Jan 13, 2015 #1
    I have a situation where I need to figure how much force it will take to stop an 8,000lb tractormoving at a max speed of 5mph in somewhere around a foot. It will not be an impact stop as there is nothing for it to hit but rather a heavy brake stop. It has been quite some time since I have dealt with kinetic energy equations. Can someone check my work on this?

    m=8,000lb x 0.0310809502 lbs/slug = 248.64slugs
    v = 5m/hr x 5280ft/mile x 1hr/60min x 1min/60sec = 7.33 ft/sec

    K=0.5 * 248.64slugs * 7.33^2

    K= 6,680 ftlbs

    where F=K/d and d=1ft

    F= 6680Newtons and 1 newton = 0.224808943 pounds force

    so F= 1501.7 lbs

    If someone could verify this that would be very much appreciated
  2. jcsd
  3. Jan 13, 2015 #2
    Sorry, I see this was not the place to put this, but I also do not see how to delete it....
  4. Jan 13, 2015 #3


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    It makes a great homework problem. Leave it right where it is and don't worry.
    This is good.
    This is good.
    What are you trying to do dragging in SI units? NOT good.
    The SI conversion messed this up for you. Try it again without worrying about SI.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted