In this question, an object experiences two
forces acting on it in opposite directions.
It is moving at a constant speed. We call
these forces F_1 and F_2. Using Newton's Second
Law, F=ma, the acceleration is zero, and therefore
the resultant force on it also has to be zero.
This means that F_1 and F_2 perfectly balance
each other, and so the two forces must be
the same size.
