Physics
To measure the speed of an approaching car a police officer shines

Ultra high frequency waves on it
Microwaves on it
Radio waves on it
Light waves on it

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

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