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Motion in A Plane

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Physics Part I

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CBSE Gujarat Board Haryana Board

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Class 10 Class 12
On a certain day, rain was falling vertically with a speed 30 m/s. The wind starts blowing after some time with a speed 10 m/s in N to S direction. In which direction should a boy, waiting at bus stop, hold his umbrella to save himself from rain?

Speed of rainfall = 30 m/s

Speed of wind  = 10 m/s 

The rain will appear to fall in the direction of the resultant of rain and wind, to the boy waiting at the bus stop.

Let θ be the angle which the resultant velocity subtends with the vertical.

From the figure, 

       space space space space space space tanθ equals straight v subscript straight w over straight v subscript straight r equals 10 over 30 equals 1 third

                  straight theta equals 18 degree 26 apostrophe

Therefore, the boy should hold the umbrella at angle 18 degree 26 apostropheorth of vertical.


Give three examples of scalar quantities.

Mass, temperature and energy

What is a scalar quantity?

A physical quantity that requires only magnitude for its complete specification is called a scalar quantity.

Give three examples of vector quantities.

Force, impulse and momentum.

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. 


What is a vector quantity?

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

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