A point mass is shot vertically up from ground level with a velocity of $4$ m/s at time, $t=0$. It loses $20 \%$ of its impact velocity after each collision with the ground. Assuming that the acceleration due to gravity is $10 \: m/s^2$ and that air resistance is negligible, the mass stops  bouncing and comes to complete rest on the ground after a total time (in seconds) of

1. $1$
2. $2$
3. $4$
4. $\infty$