A stone is thrown from the surface of the earth vertically upwards at a speed of 10 m, s. At what height will the kinetic

A stone is thrown from the surface of the earth vertically upwards at a speed of 10 m, s. At what height will the kinetic energy of the stone decrease by 5 times compared to the initial one?

we use the law of conservation of energy:
E kinetic maximum = E potential energy + E kinetic / 5
speed = 10 m / s squared
m * V squared / 2 = m * g * h + m * V squared / 10
V squared / 2 = g * h + V squared / 10
10 squared / 2 = 10 * h + 10 squared / 1 0
100/2 = 10 * h + 100/1 0
50 = 10 * h + 10
we transfer the known ones to one side, and the unknowns to the other side, when transferring values, the signs change to the opposite, then we get
10 * h = 50 – 10 = 40
h = 4 meters
answer: 4 meters