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: Crate motion question

  1. Jul 7, 2006 #1
    Just wanted to make sure if I did this right:

    Two crates of mass 12kg and 20kg are pushed across a smooth floor together, the 20kg crate in front of the 12kg crate. Their acceleration is 1.75m/s^2. What is the action reaction force between the crates?


    then F for the 12kg block = 21N, 56-21=35N, therefore the force between the crates is 35N
  2. jcsd
  3. Jul 7, 2006 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    It is not "F", the applied force on the 12kg crate that is 21N. The applied force F on this crate is 56N!!

    However, m*a for the 12kg crate equals 21N, and hence, the reaction force R between the two crates has magnitude 56N-21N=35N
  4. Jul 7, 2006 #3
    Hi Hollysmoke,
    Since the 20 kg crate is in front of the 12 kg crate, the 12kg crate must push the other crate with a force that is sufficient to communicate an acceleration of 1.75 m/s^2.
    Force that must act on the 20 kg crate must be equal to it's mass times its acceleration = 20kg x 1.75 m/s^2 = 35N.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook