Physics
On a clean glass plate a drop of water spreads to form a thin layer whereas a drop of mercury remains almost spherical because:

density of mercury is greater than that of water.
mercury is a metal.
cohesion of mercury is greater than its adhesion with glass.
cohesion of water is greater than its adhesion with glass.

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Physics
Railway tracks are banked on curves

necessary centrifugal force may be obtained from the horizontal component weight of the train
necessary centripetal force may be obtained from the horizontal component of the weight of the train
to avoid frictional force between the tracks and wheels
the train may not fly off in the opposite direction

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