Question

Student of class twelve presented a gift to their school in the form of an electric lamp in the shape of a glass hemispherical base surmounted by a metalic cylinder top of same radius 21 centimeter and hight 3.5centimeter the top was silver coated andthe glass surface was painted red. find

cost of silver coating the top at ₹5 per 100 cm2


surface area to be painted red. ​

Answer 1

Answer:Cost of silver coating = 92.4Rs

surface area to be painted red = 2772cm2

Step-by-step explanation:

Area to be coated with silver = 2πrh+πr2=πr(2h+r)

=22/7×21(7+21)

=66×28

=1848cm²

Cost of silver coating=1848/100 × 5

=92.5Rs

Surface area to be painted red = 2πr²

=2×22/7×21×21

=2772cm²

Answer 2

Rs.138.6 and 462 cm²

Step-by-step explanation:

The top hemisphere has surface area 2πr² and it is painted with silver coating.

So, the surface area = $2 \times \frac{22}{7}\times 21^{2} = 2772$ sq. cm.

Therefore, the cost of silver coating the top at Rs.5 per 100 cm² will be = $\frac{2772 \times 5}{100} = 138.6$ rupees. (Answer)

Again, the curved surface area of the cylinder with a radius 21 cm and height 3.5 cm will be = 2πrh = $2 \times \frac{22}{7} \times 21 \times 3.5 = 462$ cm² (Answer)