Physics
It is easier to roll a barrel full of coal tar than to pull it because

the full weight of the barrel comes into play when it is pulled
the rolling friction is much less than the sliding friction
coal tar is a liquid and it flows in the barrel when it is rolled
more surface area of the barrel is in contact with the road when it is pulled

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Physics
Which of the following occurred first ?

Max Planck unveiled the Quantum Theory
Guglielmo Marconi sent out the first wireless signals
Wright Brothers successfully flew an aircraft
Albert Einstein propounded the General Theory of Relativity

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