1.

Water falling from a `50m` high fall is to be used for generating electric energy. If `8xx10^5kg` in water falls per hour and half the gravitational potential energy can be converted into electric energy, how many `100W` lamps can be lit?

Answer» `h=50m`, `m=1.8xx10^5kg`, `P=100W`
`PE=mgh=1.8xx10^5xx10xx50=900xx10^5Jh^-1`
Because half the potential energy is converted into electricity
Electrical energy `=1/2PE=450xx10^5Jh^-1`
So, power in watt `(Js^-1)=(450xx10^5)//(3600)`
The number of `100W` lamps that can be lit
`=(450xx10^5)/(3600xx100)=125`


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