A proton is projected from the origin making an angle of 60° with the x-axis. A magnetic field B→=2i^ tesla exists in that region of space. The proton passes through the x-axis for the first time at a distance of 50 cm from the origin. When an α - particle is projected from the origin with same speed making an angle of 30° with the x-axis in the same magnetic field, it passes though the x-axis at a distance ‘d’ from the origin. Then the value of ‘d’ is