Question

Q7) A tennis ball is thrown up and reaches a height of 4.05 m before coming down. What
was its initial velocity? How much total time will it take to come down? Assume g = 10 m/s2​

Answer 1

$Displacement (s) = 4.05 m \\ g = -10 m/s² \\ Final \: velocity (v) = 0 m/s \\ To \: find: Initial \: velocity (u) = ? \\ t \: total (t) = ? \\ Formula: v² = u² + 2gs, u + gt \\ t \: total = 2 × t \\ Solution: v² =u² + 2gs \\ 0² = u² + 2 × (-10) × 4.05 \\ 0 = u² - 81 \\ u² = 81 \\ u = 9 m/s \\ v = u + gt \\ 0 = 9 + (-10) × t \\ 10 t = 9 \\ t = 0.9 s$

$Time \: of \: ascent = \\ Time \: of \: descent \: t \: total = 2t \\ = 2 × 0.9 = 1.8 s$

$The \: initial \: velocity \: was \\ \: 9 m/s \: and \: total \: time \: taken \: to \\ \: come \: down, is \: 1.8 s......$

Hope IT Helps you