Physics
posted by Aquile .
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?

a. = V = Vo + g*t
Tr = (VVo)/g = (015)/9.8 = 1.53 s. =
Rise time.
Tf = Tr = 1.53 s. = Fall time.
T = Tr + Tf = 1.53 + 1.53 = 3.06 s. =
Time to return to window level.
b. H = Vo*t + 0.5g*t^2 = 20 m.
15*t + 4.9t^2 = 20
4.9t^2 + 15t  20 = 0
Use Quadratic Formula.
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. 
Correction:
c. V^2 = (15)^2 + 19.6*20 = 617
V = 24.8 m/s.