First slide

Projectile motion

Question

A student throws soft balls out of the window at different angles to the horizontal. All soft balls have the same initial speed $v = 10 \sqrt{3} {ms}^{- 1}$ . It turns out that all soft balls landing velocities make angles 30^o or greater with the horizontal. Find the height h (in m) of the window above the ground. $Take g = 10 {ms}^{- 2}$

Moderate

Solution

Minimum $θ$ implies minimum $V_{fy}$ and maximum $V_{fx}$ . In order to have the mentioned situation, the rock has to be launched horizontally.
$v_{y} = \sqrt{2 gh}$
$\tan 30^{\circ} = \frac{v_{y}}{v} = \frac{\sqrt{2 \times 10 \times h}}{10 \sqrt{3}}, h = 5 m$

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