The density of a new planet is twice that of earth. The acceleration due to gravity at the surface of the planet is equal to that at the surface of earth. If $R$ is the radius of earth, then radius of the planet would be

A particle is moving in a circle with uniform speed. It has constant

A string has mass per unit length of $10^{-6} \mathrm{~kg} / \mathrm{cm}$ The equation of simple harmonic wave produced in it is $\mathrm{Y}=0.2 \sin (2 \mathrm{x}+80 \mathrm{t}) \mathrm{m}$. The tension in the string is

A spring has length L and force constant K . It is cut into two springs of length $L_1$ and $L_2$ such that $\mathrm{L}_1=\mathrm{NL}_2$ ( N is an integer). The force constant of spring of length $L_1$ is