An object is projected upwards with a velocity of 100 m/s. It will strike the ground after (approximately)

Explanation

To determine the total time of flight for an object projected upwards with an initial velocity, you can use the first equation of motion: v = u + at. Here, the final velocity v at the maximum height is 0, the initial velocity u is 100 m/s, and a is the acceleration due to gravity, which is approximately -9.8 m/s² (negative because it acts downward).Substituting these values, we get: 0 = 100 + (-9.8)t, solving this gives t ≈ 10.2 seconds to reach the highest point. The total time to hit the ground is twice this time (as ascent and descent times are equal), yielding approximately 20.4 seconds, which rounds to 20 seconds.Therefore, the correct answer is 20 seconds. The other options do not correctly calculate the time for total flight, either by miscalculating or considering only part of the flight duration.