# 2 boxes with 1 applied force

1. Sep 11, 2008

### fahlim003

1. The problem statement, all variables and given/known data
Box A
Mass=3.2kg
Force of Friction=2 Newtons

Box B
Mass=2.1kg
Force of Friction=1 Newton

Force applied 10.5 Newtons [horizontally].

http://img162.imageshack.us/img162/7697/f1qd1.png [Broken]

Q. Find the magnitude of the force of contact between the two boxes.

2. Relevant equations
F=ma

3. The attempt at a solution

I need to find acceleration first since the Force of Friction of both boxes is not greater than the Force Applied.

Fnet=(mA+mB)a

(mA+mB)a=Fa-(FfA+FfB)
(3.2kg+2.1kg)a=10.5N-(2N+1N)
(5.3kg)a=10.5N-(3N)
a=10.5N-(3N)/5.3kg
a=7.5N/5.3kg
a=1.415m/s/s

Now, I tired many, many methods of solving for this from here on, including the example from this page:https://www.physicsforums.com/showthread.php?t=202002

However, the result seems still to be wrong.
I got 7.5N as the internal force both boxes act upon eachother.

Any help is appreciated although not dire.

Last edited by a moderator: May 3, 2017
2. Sep 12, 2008

### alphysicist

Hi fahlim003,

I'm not getting the answer of 7.5N. Can you show how you got it?