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Class 10 Class 12
Two trains 120 m and 80 m in length are running in opposite direction with velocities 42 km/hr and 30 km/hr. In what time they will complete cross each other?

Relative velocity of one train w.r.t second,

= 42 - (-30)

= 72 km /hr

= 20 m/s

Total distance to be travelled = 120 + 80 = 200 m

Time taken  = 200/20 = 10 sec

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What is a scalar quantity?

A physical quantity that requires only magnitude for its complete specification is called a scalar quantity.
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Give three examples of scalar quantities.

Mass, temperature and energy
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What is a vector quantity?

A physical quantity that requires direction along with magnitude, for its complete specification is called a vector quantity.
835 Views

Give three examples of vector quantities.

Force, impulse and momentum.
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What are the basic characteristics that a quantity must possess so that it may be a vector quantity?

A quantity must possess the direction and must follow the vector axioms. Any quantity that follows the vector axioms are classified as vectors.

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