IIT JEE , AIEEE Forum - Physics , Mechanics

karthik2007

When the water is at a height of 50m, it will have a potential energy of mgh joules.

It is given that 1.8 x 10⁵ kg falls per hour
So, potential energy of water per hour = mgh = 1.8 x 10⁵ x 10 x 50.

Potential energy of water per second = 9 x 10⁷/3600 Joules/Sec

But Energy/Time = Power.

So, power generated by this falling water = 9 x 107/3600 = 25 x 10³ Watt.

Since half of this is converted to electrical energy, we have 12.5 x 10³ Watt being converted to electricity.

Each bulb takes 100W, so no of bulbs = 12.5 x 10³/100 = 125 bulbs

So, answer is 125.

(If you take g = 9.8 m/s², you will get the no of bulbs as roughly 121. I have taken g as 10 m/s² here. Depending on what instructions are given in your book, use appropriate values of g).

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