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The energy levels of the electrons in a hydrogen atom according to the Bohr model are given by
E_n = -\frac{m_ee^4}{8\epsilon_0^2h^2n^2}\, n=1, 2, 3, \dots
Gravity on the Moon is about 1/6th that on the Earth. A pole-vaulter 2 metres tall can clear a 5 metres pole on the Earth. How high a pole could he clear on the Moon?
A ball whooshes down a slide and hits another ball which flies off the slide horizontally as a projectile. How far does it go?