Assuming zero initial conditions, the response y(t) of the system given below to a unit step input \(u\left( t \right)\) is ____
1
\(u\left( t \right)\)
2
\(tu\left( t \right)\)
3
\(\frac{{{t^2}}}{2}u\left( t \right)\)
4
\({e^{ - t}}u\left( t \right)\)