# Physics

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A ball is thrown upwards at 15m/s from a window 20 metres above the ground. Find: a)How long the ball the takes to reach the level of the window
b)How much longer it takes to reach the ground?
c)What speed it takes to reach the ground?

• Physics -

a. = V = Vo + g*t
Tr = (V-Vo)/g = (0-15)/-9.8 = 1.53 s. =
Rise time.
Tf = Tr = 1.53 s. = Fall time.
T = Tr + Tf = 1.53 + 1.53 = 3.06 s. =

b. H = Vo*t + 0.5g*t^2 = 20 m.
15*t + 4.9t^2 = 20
4.9t^2 + 15t - 20 = 0
T = 1.0 s. To reach Gnd.

c. V^2 = Vo^2 + 2g*h.
V^2 = 15 + 19.6*20 = 392
V = 19.8 m/s.

• Physics -

Correction:
c. V^2 = (15)^2 + 19.6*20 = 617
V = 24.8 m/s.

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