From the top of a tower of a height 40 m, a ball is projected upwards with a speed of 20 m/s at an angle of elevation of 30°. The ratio of the total time taken by the ball to hit the ground to its time of flight (time taken to come back to the same elevation) is (Take g = 10 m/s2)
2 : 1
The time of flight The initial downward velocity = 20 sin 30° = 10 ms-1. The time taken to fall through a height of 40 m with velocity 10 ms-1 is given by
or t2 + 2t – 8 = 0
which gives t = 2s. Hence the total time to hit the ground
= tf + t = 2 + 2 = 4s
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