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Physics Part I

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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.


What is a scalar quantity?

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

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.

Give three examples of scalar quantities.

Mass, temperature and energy

Give three examples of vector quantities.

Force, impulse and momentum.