How long does a ball take to reach the ground 7 m below, if it is thrown straight up with an initial speed of 2.00 m/s?

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How long does a ball take to reach the ground 7 m below, if it is thrown straight up with an initial speed of 2.00 m/s?

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Answer 1 · 2014-10-29T07:49:08

u=2m/s

a= -g = -10m/ $s^{2}$ $s^2$

S= -7m

t= ?

$S = u t + \frac{1}{2} a t^{2}$ $S= ut + 1/2 at^2$
$- 7 = 2 t + \frac{1}{2} (- 10) t^{2}$ $-7= 2t + 1/2 (-10) t^2$
$2 t - 5 t^{2} + 7 = 0$ $2t - 5t^2 +7 =0$
$5 t^{2} - 2 t - 7 = 0$ $5t^2 -2t - 7 =0$
$t = \frac{7}{5}, - 1$ $t = 7/5 , -1$

As t can't be negative, t = 7/5 s = 1.4s.

Therefore, t = 1.4s

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How long does a ball take to reach the ground 7 m below, if it is thrown straight up with an initial speed of 2.00 m/s?

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