NCERT Class 9 Solutions: Surface Areas and Volumes (Chapter 13) Exercise 13.8 – Part 3
Q-7 Find the volume of a sphere whose surface area is .
Consider radius of the sphere to be
We know that, surface area
Since we know radius r, volume is =
Q-8 A dome of a building is in the form of a hemisphere. From inside, it was white-washed at the cost of If the cost of white-washing is per square metre, find the
Inside surface area of the dome.
Volume of the air inside the dome.
We know that,
Inside of the building is white-washed at the cost of
Rate of white washing is per square metre.
Therefore, inside surface area of the dome
Let, radius of the dome be , then surface area (which we know from I. above)
Volume of the air inside the dome = Volume of the dome. However, since we know the radius, we can now calculate the volume =