The velocity of a wave is given by $v = \sqrt{\frac{T}{\mu}} + ax^2$, where $T$ is tension, $\mu$ is linear density, and $x$ is displacement. What are the dimensions of $a$?

One  light  year  is defined as the distance travelled by light in one year. The speed of light is $3 imes {10^8}{\rm{m}}{{\rm{s}}^{ - 1}}$. The same in metre is

Light year is a unit of