A stone is thrown vertically upward with a speed of 24.0 m/s.
(a) How fast is it moving when it reaches a height of 13.0m?
(b) How much time is required to reach this height?
Answer: Let u = unitial velocity = 24 m/s
(a) v2 - u2 = 2as
v2 -u2 = - 2gh
v2= u2 - 2gh = (24)2 - 2 * 9.8* 13 = 321.2
velocity atthe height of 13 m , v = ? 321.2 = 17.92m/s
(b) s = ut + ( 1/2) at2
h = u t - ( 1/2) gt2
13 = 24 t - 4.9t2
4.9 t2 -24 t + 13 = 0
t = [ 24 + ( or ) - 17.92] / 9.8 = (24 - 17.92) /9.8 or ( 24 + 17.92) / 9.8
= 0.62 s ( or ) 4.28 s
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