A stone is thrown vertically upward from the top of a platform with an initial velocity of 10m/s. Calculate the height of the platform if it takes the stone 10secs to reach the ground. (g=10m/s2).​

400 meters

Calculate how much time the stone take to achieve the highest point of its trajectory:

0 - 10 = -10 • t

-10 = -10t

t = -10/-10

t = 1

So, it took 1 second to achieve the highest point of trajectory. When the stone achieves it, its have velocity 0 and begin to fall, and it takes also 1 second to return to the top of the platform, so it means that during 2 seconds of the motion. The stone achieves the same high as the platform with the velocity of 10 m/s

Now let's calculate the distance its traveled to achieve the ground:

X = 10•8 + (10•8²)/2

X = 80 + 320

X = 400 meters

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