# Physics

A ball is thrown vertically and reaches a height of 25m. What was it's initial velocity?

1. 0
2. 0
3. 10
1. v = Vi - g t
at top v = 0
so
0 = Vi - 9.81 t
Vi = 9.81 t

h = Hi + Vi t - 4.9 t^2
but t = Vi/9.81
so
25 = Vi (Vi/9.81) - 4.9 (Vi^2/9.81^2)
25 = Vi^2 (.102 - .051)
Vi^2 = 490
Vi = 22.1
alternatively
(1/2) m Vi^2 = m g h
or
Vi = sqrt (2 g h)
= 22.14

1. 0
2. 0
posted by Damon

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