Question

A circular tunnel of diameter of 2m and length 1.4km is dug out find the cost of plastering it at rs 150per 100m2

Answer 1

Solution :-

Diameter of the circular tunnel = 2 m 

Then, radius of the circular tunnel = 2/2 = 1m

Length or height of the circular tunnel = 1.4 km or 1400 m

As the circular tunnel is in the shape of a right circular cylinder.

Curved surface area of cylinder = 2πrh

⇒ 2*22/7*1*1400

= 8800 m²

Cost of plastering the tunnel = Rs. 150 per 100 m²

Total cost of plastering = (8800*150)/100

= Rs. 13200

So, the total cost of plastering will be Rs. 13200

Answer.

Answer 2

Circular tunnel is in the shape of a cylinder.

Given:
Diameter of the circular tunnel (d)= 2 m
radius of the circular tunnel(r) = d/2=2/2 = 1m

height of the circular tunnel(h) = 1.4 km= 1.4× 1000 = 1400 m

[1km = 1000 m]

Curved surface area of cylinder (CSA)= 2πrh

CSA of a Cylinder= 2×(22/7)×1×1400
= 2× 22× 200= 44×200

CSA of a Cylinder= 8800 m²

Cost of plastering the tunnel = ₹150 per 100 m² (given)

Total cost of plastering = CSA of Cylinder × rate
Total cost of plastering =(8800×150)/100
=88×150
= ₹ 13200

Hence, the total cost of plastering = ₹ 13200.

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