A

Step 1: Understand the energy conversion in the pendulum. The bob at its highest point has potential energy which converts to kinetic energy at the mean position.
Step 2: Calculate the potential energy (PE) at the height of 10 cm (0.1 m):
PE = mgh = m * 980 * 0.1 = 98m (in cm·s^-2 for m = mass in grams).
Step 3: At the mean position, all potential energy converts to kinetic energy (KE):
KE = \frac{1}{2} mv^2 = 98m.
Step 4: Equate PE and KE: \frac{1}{2} mv^2 = 98m.
Step 5: Cancel m (assuming m ≠ 0): \frac{1}{2} v^2 = 98.
Step 6: Rearrange the equation to find v: v^2 = 196, thus v = \sqrt{196} = 14 cm/s.
Therefore, the speed of the bob at the mean position is 14 cm/s.