An apple weighing 190 g falls from a tree from a height of 4 m. What kinetic energy will it have at a height of 1.5 m from the ground?
m = 190 g = 0.19 kg.
g = 9.8 m / s2.
h1 = 4 m.
h2 = 1.5 m.
Let’s use the law of conservation of total mechanical energy.
The total mechanical energy E is the sum of the kinetic Ek and the potential energy of the body En: E = Ek + En.
Potential En and kinetic Ek energy of the body is determined by the formulas: En = m * g * h, Ek = m * V2 / 2.
At the moment of separation, the total mechanical energy of the body E consists only of potential energy: En1 = m * g * h1.
When falling, the potential energy of the apple decreases and turns into kinetic energy, but the total mechanical energy does not change.
En1 = En2 + Ek2.
Ek2 = En1 – En2 = m * g * h1 – m * g * h2 = m * g * (h1 – h2).
Ek2 = 0.19 kg * 9.8 m / s2 * (4 m – 1.5 m) = 4.655 J.
Answer: at a height, the apple will have kinetic energy Ek2 = 4.655 J.
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