Question

It was decided to put 20street lights on the road. Each light was in the shape of a cone mountedon acylinder having base radius 40cm.

Answer 1

Answer:

full question please so I answer the question

Answer 2

Total surface area of street light is $\mathbf{352000 \ cm^{2}}$ . Total cost of install of street light is 52800 rupees.

Explanation:

1. Given data

   Radius of cylinder = Radius of cone = 40 cm

   Height of cylinder (H) = 45 cm

   Height of cone (h) = 30 cm

   Rate of cost of installation = 15 rupees per 100 $\mathbf{(cm^{2})}$

   Number of street light (N) = 20

2. Slant height of cone $\mathbf{(L)=\sqrt{h^{2}+R^{2}}}$

⇒Slant height of cone $\mathbf{(L)=\sqrt{30^{2}+40^{2}}}$

⇒Slant height of cone $\mathbf{(L)=\sqrt{2500}}$

⇒Slant height of cone $\mathbf{(L)=50 \ cm}$       ...1)

3. Lateral surface area of each cylinder $\mathbf{=2\pi RH}$       ...2)

   And

   Curved surface area of each cone $\mathbf{=\pi RL}$      ...3)

 

   Total surface area of each street light $\mathbf{=2\pi RH+\pi RL}$

⇒ Total surface area of each street light $\mathbf{=\pi R (2H+L)}$      ...4)

4.  

⇒ Total surface area of 20 street light $\mathbf{=N\pi R (2H+L)}$      ...5)

⇒ Total surface area of 20 street light $\mathbf{=20\times \frac{22}{7}\times 40(2\times 45+50)}$

⇒ Total surface area of 20 street light $\mathbf{=20\times \frac{22}{7}\times 40\times 140}$

⇒ Total surface area of 20 street light $\mathbf{=352000 \ cm^{2}}$    ...6)

5.

Total surface cost of 20 street light $\mathbf{=Total \ surface \ area \times Rate}$   ...7)

   

   Total surface cost of 20 street light$\mathbf{=352000\times \frac{15}{100}=52800 \ rupees}$