A cosmic ray proton enters Earth's atmosphere moving straight down at 2.98 x 10^8 m/s. Earth's magnetic field at this location points northward but makes an angle of 23.7 degree with the vertical. The force on the proton has a magnitude of 8.74 x 10^-16 N. Find the strength of Earth's magnetic field at this location.

A cosmic ray proton enters Earth's atmosphere moving straight down at 2.98 x 10^8 m/s. Earth's magnetic field at this location points northward but makes an angle of 23.7 degree with the vertical. The force on the proton has a magnitude of 8.74 x 10^-16 N. Find the strength of Earth's magnetic field at this location.