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# A ball is thrown vertically upwards from ground and a student gazing out of window sees it moving upward past him at 5 m/s. The window is 10 m above the ground.Find the maximum height of the ball.

$(a)\;11.25 m \quad (b)\;12.15 m \quad (c)\;10.50m \quad (d)\;14.25m$

$v^2-u^2=2as$
$u=? \quad v=5 m/s\quad s=10m\quad a=-10$
Therefore $5^2-u^2=2 \times (-10) \times 10$
$u^2=225m/s$
$Maximum\; height=h=\large\frac{u^2}{2g}$
$=11.25m$
Hence a is the correct answer.
edited May 23, 2014