Using the 2nd equation of motion;
= s = ut + ½at²
= 40 = u×2 + ½ × 6 × 2²
= 40 = 2u + 3 × 4
= 40 - 12 = 2u
= 28/2 = u
= 14 m/s = u
And its done! Simple isn't? :P
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