The magnitude of the frictional force is B) 300 N
Explanation:
For this problem, we just have to consider the forces acting on the box in the horizontal direction.
There are only two forces in this direction:
- The pull applied by the man, of magnitude F=300 N, forward
- The frictional force, , acting backward
So the equation of motion for the box is
where
m is the mass of the box
a is its acceleration
However, the box is at rest, so its acceleration is zero:
a = 0
This means therefore that
And so the magnitude of the frictional force is equal to the pulling force:
Learn more about friction:
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