**Solution:**

We have been given that u = 3 m s^{–1} and v = 7 m s-1 , t = 2 s and m = 5 kg.

we have,

F = m ( v – u ) / t

Substitution of values in this relation gives

F = 5 kg ( 7 m s^{-1} – 3 m s^{-1}) / 2 s = 10 N.

Now, if this force is applied for a duration of 5 s (t = 5 s),

then the final velocity can be calculated by rewriting as v = u + Ft / m

On substituting the values of u, F, m

and t, we get the final velocity, v = 13 m/s^{2} .