Two balls $\mathrm{X}$ and $\mathrm{Y}$ are thrown from top of tower one vertically upward and other vertically downward with same speed. If times taken by them to reach the ground are $6 \mathrm{s}$ and $2 \mathrm{s}$ respectively, then the height of the tower and initial speed of each ball are $\left(\mathrm{g}=10 \mathrm{m} {\mathrm{s}}^{-2}\right)$

A particle starts moving from rest on a straight line. Its acceleration a verses time $\mathrm{t}$ is shown in the figure. The speed of the particle is maximum at the instant

Figure shows the graph of $x$-coordinate of a particle moving along $x$-axis as a function of time. Average velocity during $t=0$ to $4 \mathrm{s}$ and instantaneous velocity at $t=4.113 \mathrm{s}$ respectively will be