The magnitude of the friction force on the box is 36N.
The force applied by the man to push the box of mass 80kg is 180N.
the acceleration of the block is 1.80m/s².
Now, we know,
Acceleration = Net force/mass
A = F/M
Now, the net force will be applied force minus frictional force.
So, if the frictional force is Fr and the applied force is F, then we can write,
a = F-Fr/M
Putting values,
1.80 = 180-Fr/80
Fr = 36N.
So, the frictional force is 36N in magnitude.
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