Question

A car starts to move at rest. It travels first 10 seconds with a constant acceleration of 2ms^-2 and the next one minute with the obtained constant velocity. During the final 30 seconds, it decelerates with a constant rate and comes to rest. Find the average velocity of the car.

Answer 1

Explanation and Calculation

• The total time is $\small 10 \,s+60\,s+30\,s = 100\,s$
• And the maximum speed it achieves with that acceleration is

$\qquad\qquad \begin{aligned} \small v&=\small u+at\\ &=\small + \end{aligned}$ $\qquad\qquad \begin{aligned} \small v&=\small u+at \\ &=\small 0+2\times10\\ &=\small 20\,ms^{-1} \end{aligned}$

• Now if we draw the v - t graph if this motion then the area which is the total distance travelled is

$\qquad\qquad \begin{aligned} \small A &=\small \frac{1}{2}\times(100+60)\times v \end{aligned}$

• And then, the distance is known, you can calculate the average velocity by total distance / total time