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At Holborn underground station there is a very long escalator. Two people are in a hurry and so climb the escalator as it is moving upwards, thus adding their speed to that of the moving steps. ... How many steps are there on the escalator?

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Which Twin Is Older?

A simplified account of special relativity and the twins paradox.

Take a Message Soldier

Stage: 4 and 5 Challenge Level: Challenge Level:2 Challenge Level:2

Why do this problem?

An exercise in relative velocity and use of the distance time formula. Learners have to read and make sense of the question and interpret the information in an equation.

Key questions

What are the unknowns? What notation shall we use?

What are we asked to find out? Which unknown(s) does that involve.

What does the question tell us about distance, velocity and time?

Can we write an equation from the information given?

Are all the solutions of the equation valid? Why/why not?