What is the shortest time for which 2.5kw kettle containing 1.5kg of boiling water can be left without boiling dry

22.6 minutes

Explanation:

The energy that must be supplied to the water, in order to completely boil it, is given by:

where

m = 1.5 kg is the mass of the water at boiling temperature

is the specific latent heat of vaportization of water

Substituting into the equation, we find

The power supplied by the kettle is

We also know that power is defined as the ratio between energy supplied and time:

Therefore, the shortest time the kettle must be left on in order to completely boil the water can be found by re-arranging the previous equation:

probably not if net force is zero