Homework Help: Physics

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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