If a rock is thrown 0.8 meters into the air, how fast was it thrown

Speed, s = 3.95 m/s

Explanation:

It is given that, a rock is thrown 0.8 meters into the air. We have to find the velocity with which it is thrown.  

Using conservation of mechanical energy as :

Initial potential energy at the ground is 0 and at maximum height the final kinetic energy is 0.

So,

putting g = 9.8 m/s² and h = 0.8 m

v = 3.95 m/s

Hence, it was thrown with a speed of 3.95 m/s