A particle executes simple harmonic motion with an amplitude of $4 \mathrm{~cm}. At the mean position, velocity of the particle is 10 \mathrm{~cm} / \mathrm{s}. The distance of the particle from the mean position when its speed becomes 5 \mathrm{~cm} / \mathrm{s} is \sqrt{\alpha} \mathrm{~cm}, where \alpha=$ ________.
Choose the correct answer: