Question

A racing car, moving with constant acceleration along a straight stretch of track, passes a fixed marker A with speed of 72 km/h. Two seconds later it passes a second fixed marker B. Given that the distance AB is 45 meters, find the acceleration of the car.


A third marker C is situated near the end of this section of track. Given that the speed of the car as it passes C is 216 km/h, find the time taken by the car to travel from A to C.

Answer 1

Answer on question #64479, Physics / Mechanics$\,|\,$Relativity

Question A racing car, moving with constant acceleration along a straight stretch of track, passes a fixed marker A with speed of 72 km/h. Two seconds later it passes a second fixed marker B. Given that the distance AB is 45 meters, find the acceleration of the car.

A third marker C is situated near the end of this section of track. Given that the speed of the car as it passes C is 216 km/h, find the time taken by the car to travel from A to C.

Solution Lets write down equation of motion for these 2 sec:

$s=v_{0}t+at^{2}/2$

We know that $v_{0}=72km/h=20m/s$, $s=45$ m and $t=2$ sec. So we can find acceleration:

$a=2\frac{s-v_{0}t}{t^{2}}=2\frac{45-20\cdot 2}{2^{2}}=2.5\,m/s^{2}$

Time that is needed to travel to C can be found as

$v=v_{0}+at$

$t=\frac{v-v_{0}}{a}=\frac{60-20}{2.5}=16\,s$

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