The pressure of a fixed quantity of ideal gas is doubled. The average speed of the molecules is also doubled. The original density of the gas is $\rho$. Which is the new density of the gas? 

In an experiment, a heater of power $35 W$ is used to warm $0.240 kg$ of a liquid in an uninsulated container. The graph shows the variation of the temperature of the liquid with time.

The liquid never reaches its boiling point. Suggest why the temperature of the liquid approaches a constant value.

The volume of air in a car tyre is about $1.50\times {10}^{-2} m^3$ at a temperature of $0.0 °C$ and  pressure $250 kPa$.

Calculate the number of molecules in the tyre( in no. of Molecules).