SI unit of
(a) Force = kg m `s^(-2)` = newton
(b) Velocity = `("Displacement")/("Time") = (m)/(s) = m s^(-1)`
(c ) Density = `("Mass")/("Volume")=(kg)/(m^(3)) = kg m^(-3)`
(d) Relative density
`= ("Density of substance")/("Density of water") = (kg m^(-3))/(kg m^(-3))`
Since relative density is a ratio of two similar units, it has no units of its own.