A car covers 30 km at a uniform speed of 60 km/h and the next 30 km at a uniform speed of 40 km/h. find the total time taken.

For uniform speed, s = vt

If the car takes time t₁, to cover the first 30 km,

Þ 30 km = (60 km/h) x t₁

$\Rightarrow {\mathrm{t}}_1=\frac{30}{60}=\frac{1}{2}\mathrm{hr}=30 \min$

Similarly, if it takes time t₂ to cover the next 30 km,

Þ 30 km = (40 km/h) x t₂

$\Rightarrow {\mathrm{t}}_2=\frac{30}{40}=\frac{3}{4}\mathrm{hr}=45 \min$

The total time taken is t₁ + t₂ = 30 min + 45 min = 75 min = 1 hr 15 min.