Question

a car is moving at a speed of 40 km/s seven second after starting from rest. what was the average acceleration of the car during this time?
1. using the information in the question above. how for would have the car gone in seven seconds?

Answer 1

Given,
$$\begin{gathered} \mathrm{Initial}\mathrm{speed},\mathrm{u}=0 \\ \mathrm{Final}\mathrm{speed},\mathrm{v}=40\mathrm{km}/\mathrm{s} \\ \mathrm{Time},\mathrm{t}=7\mathrm{second} \\ \mathrm{Using}\mathrm{relation}, \\ \mathrm{v}=\mathrm{u}+\mathrm{at} \\ \mathrm{Acceleration},\mathrm{a}=\frac{\mathrm{v}-\mathrm{u}}{\mathrm{t}} \\ =\frac{40-0}{7}=5.7\mathrm{km}/{\mathrm{s}}^2 \\ \mathrm{Again}, \\ {\mathrm{v}}^2-{\mathrm{u}}^2=2\mathrm{as} \\ {40}^2-0=2\times \frac{40}{7}\times \mathrm{s} \\ 1600=2\times \frac{40}{7}\times \mathrm{s} \\ \mathrm{s}=\frac{1600\times 7}{2\times 40}=140\mathrm{km} \\ \mathrm{Thus},\mathrm{the}\mathrm{distance}\mathrm{travelled}\mathrm{in}7\mathrm{seconds}\mathrm{is}140\mathrm{km}. \end{gathered}$$