Physics
Radiocarbon is produced in the atmosphere as a result of

Action of solar radiations particularly cosmic rays on carbon dioxide present in the atmosphere.
Lightning discharge in atmosphere.
Collision between fast neutrons and nitrogen nuclei present in the atmosphere.
Action of ultraviolet light from the sun on atmospheric oxygen.

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Physics
It is easier to roll a stone up a sloping road than to lift it vertical upwards because

Work done in lifting the stone is equal to rolling it.
Work done in rolling is more than in lifting.
Work done in both is same but the rate of doing work is less in rolling.
Work done in rolling a stone is less than in lifting it.

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Physics
Siphon will fail to work if:

The level of the liquid in the two vessels are at the same height.
Both its limbs are of unequal length.
The temperature of the liquids in the two vessels are the same.
The densities of the liquid in the two vessels are equal.

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