If the length of a simple pendulum is 120cm, calculate its frequency [$\pi$ = $\frac{22}{7}$ g = 10ms$^{-2}$]

1. Analyze the question

We are asked to find the frequency ($f$) of a simple pendulum given its length ($l = 120\text{ cm}$) and the acceleration due to gravity ($g = 10\text{ ms}^{-2}$).

2. Explain the concept

The period ($T$) of a simple pendulum is given by the formula:

The frequency ($f$) is the reciprocal of the period:

Important Note: Always ensure your units are in SI units. The length must be in meters (m).

• $l = 120\text{ cm} = 1.2\text{ m}$
• $g = 10\text{ ms}^{-2}$
• $\pi = \frac{22}{7}$

3. Show the solution

Step 1: Substitute the values into the frequency formula.

Step 2: Simplify the fraction inside the square root.

Step 3: Calculate the denominator.

Step 4: Calculate the final frequency.

Rounding this value to one decimal place gives 0.5 Hz.

4. Identify the answer

Comparing our result to the options provided: A. 2.8Hz B. 1.2Hz C. 12Hz D. 0.5Hz

The calculated value aligns with option D.

5. Exam Tip

In JAMB Physics, always check your units first! Converting centimeters to meters is the most common "trap" students fall into. If you had used $120$ instead of $1.2$, your answer would have been off by a factor of 10, leading to a wrong choice. Always convert to SI units before plugging numbers into your formula.