A solid wooden toy is in the form of a hemisphere surmounted by a cone of same radius. The radius of hemisphere is 3.5 cm and the total wood used in the making of toy is . Find the height of the toy. Also, find the cost of painting the hemispherical part of the toy at the rate of ` 10 per cm2.
Let h be the height of the cone and r be radius of its base
Now, volume of the wooden toy =
According to the question,
⇒ h = 6cm
The height of the wooden toy = 6cm + 3.5 cm
= 9.5cm
Now, curved surface area of the hemispherical part = 2 π r2
= 2π × (3.5)2
=77cm2
Hence the cost of painting the hemispherical part of the toy at the rate of ` 10 per cm2 = 77 × 10 = Rs.770