An electric kettle has two coils. When one of these is switched on, the water in the kettle boils in 15 minutes. When the other is switched on, the water boils in 30 minutes.
In how many minutes will water boil if the coils are connected in series and switched on?

An electric heater takes 15 min to raise a certain quantity of water from 0°C to its boiling point.If it takes another 80 min to turn all water into steam ,find the latent heat of vaporsation of water.

A hot plate of an electric oven connected to a 220V line has two resistance coils A and B, each of 24Omega resistance, which may be used separately, in series, or in parallel. What are the currents in the three case? Amount of current when the coils are used separately.

A pump lifts 20 kg of water in one minute to a vertical height of 30m.Find the power of the pump.

Water in a canal,6 m wide and 1.5 m deep,is flowing with a speed of 10km/h.How much area will it irrigate in 30minutes,if 8cm of standing water is needed?

A man can swim with a speed of 4.0 km/h in still water. How long does he take to cross a river 1.0 km wide if the river flows steadily at 3.0 km/h and he makes his strokes normal to the river current? How far down the river does he go when he reaches the other bank?

A brass boiler has a base area of 0.15 m2 and thickness 1.0 cm. It boils water at the rate of 6.0 kg/min when placed on a gas stove. Estimate the temperature of the part of the flame in contact with the boiler. Thermal conductivity of brass = 109 J s ^-1m^- 1K^-1 , Heat of vaporisation of water = 2256 xx 10^3 J kg^-1 .