A person sitting in the ground floor of a building notices through the window, of height 1.5 m, a ball dropped from the roof of the building crosses…

A person sitting in the ground floor of a building notices through the window, of height $\displaystyle 1.5$ m, a ball dropped from the roof of the building crosses the window in $\displaystyle 0.1$ s. What is the velocity of the ball when it is at the topmost point of the window ? $\displaystyle \left(g=10 \mathrm{~m} / \mathrm{s}^2\right)$