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Motion in A Plane

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Physics Part I

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Physics

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CBSE Gujarat Board Haryana Board

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Class 10 Class 12
A man can swim with a speed of 4.0 km/hr in still water. How long does he take to cross the river 1.0 km wide if the river flows steadily at 3.0 km/hr and he makes his strokes normal to the river current? How far down the river does he go when he reaches the other bank?

Rate of flow of swimmer in the still water = 4.0 km/hr 

Width of the river = 1.0 km 

Rate of flow of river = 3.0 km/hr 
                   

Since the swimmer dives in the river normal to the flow of river, therefore time taken by swimmer to cross the river is, 

space space space space space space space straight t equals straight d over straight v subscript straight m equals fraction numerator 1 km over denominator 4 km divided by hr end fraction equals 1 fourth hr equals 15 space min

In this time the swimmer will also go down the river by distance BC due to river current. 

∴ Distance of the river travelled by the swimmer when he reaches the other bank is given by, 

 BC space equals space straight v subscript straight r straight t space
space space space space space space equals space left parenthesis 3 km divided by hr right parenthesis open parentheses 1 fourth hr close parentheses 

      equals 3 over 4 km equals 0.75 km

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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.
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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.
1212 Views

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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Give three examples of scalar quantities.

Mass, temperature and energy
769 Views

Give three examples of vector quantities.

Force, impulse and momentum.
865 Views