Physics
Stationary wave is formed by

A transverse wave superposing a longitudinal wave
Two waves of the same speed superposing
Two waves of same frequency travelling in the same direction
Two waves of same frequency travelling in the opposite direction

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Physics
Water pipes in hilly areas often burst on a cold frosty night, because

Water in the pipes freezes and on freezing water expands, so pipes break
Frost makes the pipes rusty, so they break
The material of which pipes are made contracts due to cold and so breaks
None of these

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