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Q11:
A car has two wipers which do not overlap. Each wiper has a blade of length 25 cm sweeping through an angle of 115°. Find the total area cleaned at each sweep of the blades. (Unless stated otherwise, use $\pi = \frac{22}{7}$)

Solution :

Given:

Number of wipers = $2$

Length of each wiper blade ($r$) = $25\text{ cm}$

Angle of sweep ($\theta$) = $115^\circ$

Value of $\pi = \frac{22}{7}$

To Find:

The total area cleaned by the two wipers at each sweep.

25 cm 25 cm 115° 115°

Step 1: Understanding the Geometry

Each wiper sweeps out a sector of a circle. The area of a sector of a circle with radius $r$ and central angle $\theta$ is given by the formula:

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

Step 2: Calculating the area cleaned by one wiper

Substitute the given values into the formula:

$\text{Area of one sector} = \frac{115}{360} \times \frac{22}{7} \times (25)^2$

$\text{Area of one sector} = \frac{115}{360} \times \frac{22}{7} \times 625$

Simplifying the fraction $\frac{115}{360}$ by dividing by 5: $\frac{23}{72}$

$\text{Area of one sector} = \frac{23}{72} \times \frac{22}{7} \times 625$

$\text{Area of one sector} = \frac{23 \times 11 \times 625}{36 \times 7}$ [Dividing 22 and 72 by 2]

$\text{Area of one sector} = \frac{158125}{252} \text{ cm}^2$

Step 3: Calculating the total area cleaned by two wipers

Since there are two wipers that do not overlap, the total area is twice the area of one sector:

$\text{Total Area} = 2 \times \left( \frac{158125}{252} \right)$

$\text{Total Area} = \frac{158125}{126} \text{ cm}^2$

Step 4: Final Calculation

Performing the division:

$158125 \div 126 \approx 1254.96 \text{ cm}^2$

Final Answer: The total area cleaned at each sweep of the blades is $\frac{158125}{126} \text{ cm}^2$ or approximately $1254.96 \text{ cm}^2$.


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