A lorry is travelling at $60km/h$ when the brakes are applied. Assuming that the deceleration is uniform, how far has the lorry travelled when its speed is $36km/h$ after $6$seconds.
What I did:
$s =\frac{(v+u)}2t;$
$s = 80$ $m$
But the answer to the question in the textbook is $40m$. I don't know why this happened.
I tried using the $v/t$ graph but I still arrived at the same answer.
I get the same answer as you. Either you read it wrong or there's an error in your textbook.
Average speed is $(60+36)/2 km/h=48km/h$
Time is 6 seconds: $t=6/(60\times60) hours=.0017hours$
Distance travelled equals $d=vt=48\times .0017=.08km=80m$