In the question number 67, the time taken by the ball to reach the gro

1.	In the question number 67, the time taken by the ball to reach the ground is
Answer» 2 s 3 s 5 s 7 s Solution :Let `t_1` be the time taken by the ball to reach the highest point. here, V = 0, u = `20 m s^(-1), a = - g = - 10 m s^(-2), t = t_1` As `v = u + at` `therefore0 = 20 + (-10)t_1` or `t_1 = 2 s` Taking vertical downward motion of the ball from the highest point to ground. Here, u = 0, `a = +g = 10 m s^(-2)`, S = 20 m + 25 m = 45 m, `t = t_2` As `S = ut + 1/2 at^(2)``therefore`45 = `0 + 1/2(10)t^(2)_2` `t^(2)_2 = 45 XX 2/10 = 90/10 = 9`or`t_2 = 3 s` Total time taken by the ball to reach the ground = `t_1 + t_2= 2 s + 3 s = 5 s`

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