The correct answer is C. 100 cm.
A second’s pendulum is a simple pendulum that takes one second to complete one swing, from one extreme to the other and back again. The length of a second’s pendulum is approximately 0.994 meters, or 39.37 inches. However, the exact length of a second’s pendulum depends on the local gravitational field. For example, on the Moon, where the gravitational field is about one sixth of that on Earth, a second’s pendulum would be about 5.8 meters long.
The formula for the period of a simple pendulum is:
$$T = 2\pi\sqrt{\frac{L}{g}}$$
where $T$ is the period of the pendulum in seconds, $L$ is the length of the pendulum in meters, and $g$ is the acceleration due to gravity in meters per second squared.
Substituting in the value of $g$ at Earth’s surface, we get:
$$T = 2\pi\sqrt{\frac{L}{9.80665}}$$
Solving for $L$, we get:
$$L = \frac{T^2}{4\pi^2g} = \frac{(1\text{ s})^2}{4\pi^2(9.80665\text{ m/s}^2)} = 0.994\text{ m}$$
Therefore, the length of a second’s pendulum on Earth is approximately 0.994 meters.