Posted by **Aquile** on Wednesday, February 13, 2013 at 12:19pm.

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 -
**Henry**, Friday, February 15, 2013 at 4:11pm
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. =

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.

- Physics -
**Henry**, Friday, February 15, 2013 at 4:20pm
Correction:

c. V^2 = (15)^2 + 19.6*20 = 617

V = 24.8 m/s.

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