Physics
Why are we able to hear short wave broadcasts better than long wave broadcasts ?

Short waves are more energetic than long waves.
By convention, short waves are meant for long distances, whereas long waves are reserved for short distances.
Short waves are unaffected by atmospheric disturbances.
Short wave broadcasts are made by nearby radio stations.

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Physics
A hydrogen balloon floats up because of

Air pressure decreases with decrease in weight
Air pressure decreases with decrease in height
Weight of the balloon is less than the weight of air displaced by it.
The pressure inside the balloon is more than the pressure outside it

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