KinematicsMedium
Question
A boy thrown a ball into air at $45^{\circ}$ from the horizontal to land it on a roof of a building of height H . If the ball attains maximum height in 2 s and lands on the building in 3 s after launch, then value of H is $\_\_\_\_$ m.
$$\left( g = 10\text{ }m/s^{2} \right) $$
Options
A.20
B.10
C.25
D.15
Solution
$T = \frac{2u_{y}}{g} = 4$
$${\Rightarrow u_{y} = \frac{40}{2} = 20\text{ }m/s }{y = u_{y}\Delta t - \frac{1}{2}\text{ }g(\Delta t)^{2} }{\Rightarrow H = 20 \times 3 - 5 \times 9 }{= 60 - 45 }{= 15\text{ }m}$$
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