Taking into account the various kinds of atomic coherences (Zeeman coherence, hyperfine coherence, optical coherence), we investigate the population difference between the ground state hyperfine levels (5S 1/2, F=2 and 5S 1/2, F=1) of optically pumped 87Rb atoms in a static magnetic field. The pumping laser is monochromatic and is linearly polarized perpendicular to the static magnetic field and on resonance with the (5S 1/2, F=2↔5P 1/2, F′=1) transition. We find that the incoherent collision process reduces the pumping efficiency. Changing the magnitude of the static magnetic field, we observe the Hanle effect in the population difference, and the full width at half maximum (FWHM) of the coherence dip is found to increase as the square root of the pumping laser intensity and proportionally to the population transfer rate due to collision. We interpret the Hanle effect in terms of the Zeeman coherence vanishment due to the static magnetic field, which is numerically shown to be the case.