The rate at which a piece of coal burns is much slower than the rate of burning of powdered coal of equal weight. Explain.

The time taken for the combustion of one piece of coal in air is much greater than for the combustion of powdered coal with the same mass . Explain with reasons.

Which of the following produces more heat (per unit mass) on burning? Coal or LPG.

Assertion: Smaller the organism higher is the rate of metabolism per gram weight. Reason: The heart rate of a six-month-old baby is much lower than that of an old person.

The mass of a copper steam boiler is 200 kg. It contains 100 kg of water at 25^(@)C.7xx10^(6) cal of heat is produced by burning 1 kg of coal and only 3% of it is absorbed by the boiler to heat water. How much coal is to be burnt to raise the temperature of the water in the boiler to its boiling point? Specific heat of copper ="0.09 cal.g"^(-1).^(@)C^(-1) .

Which one is the correct factor that explains the increase of rate of reaction by a catalyst

If a particle moves along the parabola y^2= 8x then the co-ordinates of the point on which the rate of change of abscissa is equal to the rate of change of ordinate, is

We know that the velocity of a gas molecule is approximately equal to the velocity of a rifle bullet,Yet,a gas molecule spends much longer time than a bullet does to travel equal distance Explain.