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Q3:
The length of the minute hand of a clock is 14 cm. Find the area swept by the minute hand in 5 minutes. (Unless stated otherwise, use $\pi = \frac{22}{7}$)

Solution :

Given:

The length of the minute hand of the clock, which acts as the radius ($r$) of the circular path, is $14\text{ cm}$.

The time duration for which the area is swept is $5\text{ minutes}$.

To Find:

The area swept by the minute hand in $5\text{ minutes}$.

r = 14 cm O θ

Step 1: Determine the angle swept by the minute hand in 60 minutes.

A minute hand completes one full rotation in $60\text{ minutes}$. A full rotation corresponds to an angle of $360^\circ$.

Angle swept in $60\text{ minutes} = 360^\circ$.

Step 2: Calculate the angle swept by the minute hand in 1 minute.

Using the unitary method:

Angle swept in $1\text{ minute} = \frac{360^\circ}{60} = 6^\circ$.

Step 3: Calculate the angle swept ($\theta$) in 5 minutes.

$\theta = 5 \times 6^\circ = 30^\circ$.

Step 4: Apply the formula for the area of a sector.

The area swept by the minute hand is the area of a sector of a circle with radius $r$ and central angle $\theta$.

Formula: $\text{Area of sector} = \frac{\theta}{360^\circ} \times \pi r^2$

[Where $\theta = 30^\circ$, $r = 14\text{ cm}$, and $\pi = \frac{22}{7}$]

Step 5: Perform the calculation.

$\text{Area} = \frac{30}{360} \times \frac{22}{7} \times 14 \times 14$

Simplify the fraction $\frac{30}{360}$:

$\text{Area} = \frac{1}{12} \times \frac{22}{7} \times 14 \times 14$

Cancel terms ($14$ divided by $7$ is $2$):

$\text{Area} = \frac{1}{12} \times 22 \times 2 \times 14$

$\text{Area} = \frac{1}{12} \times 616$

$\text{Area} = \frac{616}{12} = \frac{154}{3}\text{ cm}^2$

Converting to decimal form:

$\text{Area} \approx 51.33\text{ cm}^2$

Final Answer: The area swept by the minute hand in 5 minutes is $\frac{154}{3}\text{ cm}^2$ or approximately $51.33\text{ cm}^2$.


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