Question

Water falling from a 50-m high fall is to be used for generating electric energy. If 1·8×105 kg of water falls per hour and half the gravitational potential energy can be converted into electrical energy, how many 100 W lamps can be lit with the generated energy?

Answer 1

Answer:

122 lamps

Explanation:

The given height of the fall is,

h=50

mh=50 m

The mass of the water is,

m=1.8×105 kg

min=3600sec

t=60 min=3600 sec

The initial gravitational potential energy of the given mass of the water is,E

E=mgh

E=1.8×105×9.81×50E=882.9×105 J

Since half of the gravitational potential energy can be converted to electricity.

So, the useful energy is,

441.45×105 J

Total electrical power obtained from this energy is,P

P=441.45×1053600P=12262.5 Watt

Nearly 122 lamps can be lit from this power

Answer 2

You can light 122 bulbs.

Explanation:

Given in the question ,

Height H , = 50 m

Mass m = 1.8 × 10⁵ kg/hr  

Converting kilogram per hour to kilogram per second  

= (1.8 × 10⁵ kg) / 3600 = 50 kg/sec

Now the gravitational potential energy per sec.

= mgh

= 50 × 9.8 × 50

P.E = 24500 J.

So the electrical energy generated = 1/2  (P.E)

= 1/2  (24500  J/sec)  

= 12250 W.

So it's going to light the number of 100 W lamp.

= 12250/100  

= 122.5

Or you can light 122 bulbs.