Motion in a Straight Line Questions

A particle moves along a straight line OX. At a time $t$ (in seconds), the distance $x$ (in metres) of the particle from O is given by $x=40+12t-t^3$.How long would the particle travel before coming to rest?

Two bodies, A (of mass $1\text{kg}$) and B (of mass $3\text{kg}$) are dropped from heights of $16\text{m}$ and $25\text{m}$, respectively. The ratio of the time taken by them to reach the ground is :