An object is thrown vertically with a velocity $\mathrm{u}$. The velocity with which it strikes the ground on its return is

The following plot gives the variation of acceleration $\left(\mathrm{m}/{\mathrm{s}}^2\right)$ with time $\left(s\right)$ for an object that started from rest at time $t=0 \mathrm{s}.$ The velocity at time $t=15 \mathrm{s}\left(v_{15}\right)$ and at $25 \mathrm{s}$ $\left(V_{25}\right)$, respectively are