Question

A car on the highway travels at 90 km/hr. Express this speed in m/s.

Answer 1

90 km/h means 90,000 meters per hour. 1 hour contains 3600 seconds. Therefore, 90,000 m an hour are equivalent to

$$v=\frac{90000\text{ m/h}}{3600\text{ s/h}}=25\text{ m/s}.$$

We see a rule:

$$v_\text{m/s}=v_\text{km/h}·\frac{1000}{3600}.$$