If $450$ erg of work is done in blowing a soap bubble of radius '$r$', the additional work required to be done to blow it to a radius equal to $3r$ is

The excess pressure inside a soap bubble of radius $2.5$ cm is $48$ dyne/cm$^2$. The surface tension of soap solution in dyne /cm is

In case of liquid, if Reynold's number '$R_n$' is $1450$, then the flow of liquid will

A sphere is at temperature $600$ K. In an external environment of $200$ K, its cooling rate is R. When the temperature of the sphere falls to $400$ K then cooling rate R' will become