parabolic motion
[tex]\tt t_{max}=\dfrac{2u~sin~\alpha }{g}[/tex]
[tex]\tt h_{max}=\dfrac{u^2sin^2\alpha }{2g}[/tex]
vertically upwards ⇒ α = 90°⇒sin 90° = 1
[tex]\tt 4=\dfrac{2u}{10}\rightarrow u=20~m/s[/tex]
[tex]\tt h_{max}=\dfrac{20^2}{2.10}=\boxed{\bold{20~m}}[/tex]
