Question

A car travels along a straight line at a constant velocity of 18 m/s for 2.0 s and then accelerates at 6.0 m/s 2 for a period of 3.0 s. What is the average velocity of the car during the whole 5.0-s interval?

Answer 1

First , the car travels accross a straight line , so speed = velocity .

Now , for first 2 seconds , the average velocity is 18m / s

so distance travelled in first 2 seconds is 18×2 = 36 m

now , for next 3 seconds ,

initial velocity (u) = 18m / s

acceleration (a) = 6m/s²

time(t) = 3 sec

now we know formulae

$s = ut + (1 \div 2)at ^{2}$

= 18.3+(1/2).6.3²

= 54+(1/2)54

= 54+27

= 81 m

now , average velocity = total displacement / total time

= 81/5

= 18.2 m / s