They are called magnets poles.
By Newton's second law,
<em>n</em> + (-<em>w</em>) = 0
<em>p</em> + (-<em>f</em> ) = (20 kg) (2 m/s²)
where <em>n</em> is the magnitude of the normal force, <em>w</em> is the weight of the box, <em>p</em> is the magnitude of the applied force (<em>p</em> for <u>p</u>ush or <u>p</u>ull), and <em>f</em> is the magnitude of the friction force.
Calculate the weight of the box:
<em>w</em> = (20 kg) (9.80 m/s²) = 196 N
Then
<em>n</em> = <em>w</em> = 196 N
and
<em>f</em> = <em>µ</em> <em>n</em> = 0.5 (196 N) = 98 N
Now solve for <em>p</em> :
<em>p</em> - 98 N = 40 N
<em>p</em> = 138 N
