On a winter day the temperature of the tap water is 20∘C whereas the room temperature is 5∘C. Water is stored in a tank of capacity 0.5 m3 for household use. If it were possible to use the heat liberated by the water to lift a 10 kg mass vertically, how high can it be lifted as the water comes to the room temperature ? Take g=10 ms−2
Here m=0.5 m2=500L=500 kg
So the heat liberated during the water changes 20∘C to 5∘C
=500×4200×15
[Δθ=20−5=15]
=500×4200×15
=75×420×1000
=31500×1000
Let the height = h
the required work
=mgh=10×10×h=100 h
But, 100 h = 3150000
⇒h=315000 m=315 km