The formula to find kinetic energy is -
\(K.E. = \frac{1}{2}*m* v^{2}\)
Where,
\(m = mass\)
and
\(v = velocity\)
So, putting the values in the formula we get -
\(40 = \frac{1}{2} *6*v^{2}\)
\(\frac{40}{3} = v^{2}\)
\(\sqrt \frac{40}{3} = 3.6514 m/s\)