Question

# A ball is thrown upwards with an initial velocity of 20 ms−1. Find the time of flight and the maximum height reached by the body respectively. (g=10 ms−2)4 s 20 m5 s 25 m4 s 24 m5 s 30 m

Solution

## The correct option is A 4 s 20 mGiven: Initial velocity, u=20 ms−1 Acceleration due to gravity, g=−10 ms−2 Upward direction is taken as positive. At maximum height, velocity will be zero, (v = 0) as the ball will change the direction of motion. Let the maximum height be H. Using third equation of motion,  v2=u2+2as 02=202+2×(−10)×H H=20 m When the ball returns to the initial point, net displacement is zero. Let the time of flight be T. Using second equation of motion, we get: s=ut+12at2 0=20×T+12×(−10)×T2 T=0 or T=4 s Time of flight is more than zero. So, it is 4 s.

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