Question

The internal and external radius of a hollow cylinder are 7cm and 14 cm. If the height is 21 cm,find the total surface area to be painted on internally, externally as well as along the circular ends.​

Answer 1

Answer:

T S A to be painted = C SA of in.cylinder+CSA of ex.cylinder+2(area of ring)

Step-by-step explanation:

=2πrh+2πRh+2π(R^2-r^2)

=2×22/7×7×21+2×22/7×14×21+2×22/7(14^2-7^2)

=2×22×21+2×22×2×21+2×22/7(196-49)

=2×22×21(1+2+1)

=2×22×21×4

=3696cmsq