The force exerted by a magnetic field of intensity B on a wire of length L is:

where I is the current in the wire and

is the angle between the wire and the direction of B.
In our problem, the length of the wire is L=260 m, the current is I=115 A, the intensity of the Earth's magnetic field is

and the angle between the wire and B is

, and by substituting these numbers in the previous expression we can find the magnitude of the force:
