ANSWER:
50 km/hr
STEP-BY-STEP EXPLANATION:
Given:
Final speed (v) = 65 km/hr
Acceleration (a) = 3 km/hr/sec
Time (t) = 5 sec
We have the following formula, we substitute and solve for the initial speed, just like this:
[tex]\begin{gathered} v=u+at \\ \\ 65=u+3\cdot5 \\ \\ u=65-15 \\ \\ u=50\text{ km/hr} \end{gathered}[/tex]Therefore, the initial speed is 50 km/hr.