The speed of a car is 72 km h^-1. Express it in m s^-1.

As,

$72 \text {km h}^{-1} = \dfrac{72 \text {km}}{1 \text {h}} = \dfrac {72 \times 1000 \text {m}}{(60 \times 60) \text {s}} \\[0.5em] \Rightarrow 72 \text {km h}^{-1} = \dfrac {72 \times 10 \text {m}}{(6 \times 6 )\text {s}} \\[0.5em] \Rightarrow 72 \text {\text {km h}}^{-1} = \dfrac {20 \times \text {m}}{\text {s}} \\[0.5em]$

Hence, 72km h^-1 is equal to 20 m s^-1.