A child and sled with a combined mass of 13.2 kg slide down a friction less hill that is 6.9 m high. If the sled starts from rest, how much kinetic energy will they have at the bottom of the hill?

as we know our atmosphere or air have different levels. every level has other gasses, and every gas has another permeability. when the light comes from lower permeability to higher permeability, it changes its direction. so that means that when the light comes from the moon to the earth, it changes it's direction many more times. it basically means that the shape of the light part of the moon is changed on the earth.

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