Question

From a solid hemisphere whose radius is 2.1 cm, a conical cavity of the same
height and same diameter is hollowed out. Find the total surface area of the
remaining solid to the nearest cm' and also find out the cost of painting the
remaining solid at the rate of Rs.1.25 per square cm. (Use V2 = 141)
​

Answer 1

Answer:

The cost of the painting is 58.5 Rs

Step-by-step explanation:

Hemisphere = "r" = 2.1 cm

Means h = 2.1 cm

Now find the value of l.

l = √ (h)^2 + (r)^2

l = √ (2.1)^2 + (2.1)2

 =√  4.41 + 4.41 = √ 882/100

 = √ 2 x 7 x 3 x 3 x 7 / 100

 = 7 x 3 √ 2 / 10 = 21 √ 2

Since √ 2 = 1.41

= 29.64/10 = 2.964

l = 2.964 cm

Now

TSA . CSA (of hemisphere + cone)

= 2π r^2 + π rl

= π r ( 2r + l) = 22/7 x 21/10 (4.2 + 2.9)

= 66/10 x 7.1 = 4686/10

= TSA x 46.86 cm^2 x 1.25

Cost = 58.5 Rs