a
Given

\(M =5\,kg\)

\(P _{ i }=10\,kg\,m / s \text { (initial momentum) }\)

\(\text { Impulse }= F \Delta t =\Delta P = P _{ f }- P _{ i }\)

\(2 \times 5= P _{ f }-10\)

\(P _{ f }=20\,kg\,m / s \text { (final momentum) }\)

\(\text { Increase in } KE = KE _{ f }- KE _{ i }\)

\(=\frac{ P _{ f }^2}{2 m }-\frac{ P _{ i }^2}{2\,m }\)

\(=\frac{400}{2 \times 5}-\frac{100}{2 \times 5}=40-10=30\,J\)