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Important questions based on NCERT syllabus for Chapter 13 - Surface Areas and Volumes:
Question 1: A cylindrical saline bottle has a radius of 7 cm and height of 20 cm. If the saline is released at a rate of 10 cubic cm per second, in approximately how many minutes does the saline bottle get emptied?
r = 7,h = 20
Volume of the saline bottle = πr^2h
= 22/7 × 72 × 20
No. of seconds needed = 3080/10 = 308s
308 s = 5.13 min
Question 2: Raghu had to make a cylindrical tube with an aluminium cover. What is the area of the aluminium sheet he needs to cover the tube if the tube has a length of 1m and base radius 3.5cm? (Take π = 22/7)
r = 3.5cm,h = 1m = 100cm
Area of Aluminium sheet required = curved surface area of the tube
= 2 × 22/7 × 3.5 × 100
Question 3: 14. A hemispherical bowl made of brass has inner radius of 3.5 cm. Find the cost of tin-plating the inner part of the bowl as well as tin plating a plate that exactly fits as a lid on bowl. Tin plating is done at the rate of Rs.10 per 100 sq.cm.
Surface area that has to be plated = Curved surface area of the hemisphere bowl + surface area of the plate
= 2πr^2 + πr^2
= 2 × 22/7 × 3.52 + 22/7 × 3.52
= 3 × 22/7 × 3.52
Hence cost of tin plating = 115.5 × 10/100