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Lunar Leaper

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?

Which Twin Is Older?

A simplified account of special relativity and the twins paradox.


A ball whooshes down a slide and hits another ball which flies off the slide horizontally as a projectile. How far does it go?

Escape from Planet Earth

Age 16 to 18 Challenge Level:

At what distance from the earth would an object have zero gravitational potential energy?

How fast would the balls need to be thrown so that they only just reach this point?