Constant motion

The car has undergone constant motion, traveling 120 km in 1 hour and 30 minutes. Determine its average speed. Also, determine how long the car drove in the first 20 minutes and 50 minutes after starting the move.

Correct answer:

v =  80 km/h
s₁ =  26.6667 km
s₂ =  66.6667 km

Step-by-step explanation:

$$\begin{gathered} s=120\text{km} \\ t=1+30/60=\frac{3}{2}=1.5\text{h} \\ v=s/t=120/1.5=80\text{km/h} \end{gathered}$$

$$\begin{gathered} t_1=20\text{min}\to \text{h}=20:60\text{h}=0.33333\text{h} \\ {s}_1=v\cdot t_1=80\cdot 0.3333=26.6667\text{km} \end{gathered}$$

$$\begin{gathered} t_2=50\text{min}\to \text{h}=50:60\text{h}=0.83333\text{h} \\ {s}_2=v\cdot t_2=80\cdot 0.8333=66.6667\text{km} \end{gathered}$$

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