Question

a body is moving with a velocity of 12 m/s and its comes to rest in 18m. what was the acceleration.

Answer 1

Here we've 
=> u=12 m/s , v=0 m/s and s=18 m

So we can use the equation
$v^{2} - v^{2} =2as \\ 0^2-12^2=2*a*18 \\a= \frac{144}{36} \\ a=4m/s^2$
Therefore the acceleration is 4 m/s²

Answer 2

v² - u² = 2as
----------------------------
v = 0
u =12m/s
s= 18

0 - 12² = 2(a)18

= -144 = 36s

a = 144/36

= -4m/s²
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-ve indicates the body is having deceleration