Final answer:
If a pendulum in an accelerating elevator downward at 5 m/s², the effective acceleration decreases, leading to a new frequency that is the original frequency divided by √2. The correct option is C.
Step-by-step explanation:
The oscillation frequency of a pendulum is determined by its length and the effective acceleration due to gravity acting on it. On Earth's surface, this acceleration is approximately 9.81 m/s², but if the pendulum is in an elevator that is accelerating downward at 5 m/s², the effective acceleration decreases.
Therefore, the formula to calculate the new frequency involves the square root of the ratio of the new effective acceleration to the standard acceleration due to gravity, which is g' = g - a, where g is the acceleration due to gravity (9.81 m/s²) and a is the acceleration of the elevator.
The new frequency (f') is then related to the old frequency (f) by the equation f' = f √(g'/g). Plugging in the values, we get g' = 9.81 m/s² - 5 m/s² = 4.81 m/s², therefore, f' = f √(4.81/9.81), which is approximately f divided by √2. Hence, the correct answer is C: The oscillation frequency is divided by √2.