Question

What if all the people jump at same time

Answer 1

If all the people jump at same time then all will step down in the same time ...... And if they jump from a slope or cliff then they all will die .....
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HOPE IT HELPS YOU

Answer 2

WIth roughly 7 billion people on Earth, who have a total weight of approximately 800 billion pounds (363 billion kg).  So if they all jump at the same time from their current positions, nothing will happen, because people are spread somewhat equally around the planet's spherical surface. All our lift-offs and impacts would cancel each other out, resulting in zero net force on the Earth, according to work by physicist Rhett Allain  However, if everyone congregate together in one place and then jump, Allain found that our jump would push on the Earth ever so slightly, giving it a recoil speed of 2.6 x 10^-13 m/s. That is, in one second, Earth would move about a hundredth of the radius of a single hydrogen atom.