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Class 10 Class 12
Two cars A and B are moving with same speed 30km/hr in same direction with car B 5km behind the car A. Another car C moving in opposite direction crosses the two cars at an interval of 4 minutes. Find the speed of car C.

Let the car C be moving with velocity u km/hr.

Car B is 5 km behind the car A, therefore when the car C crosses car A, it is 5 km from car B.

Let us take left direction as positive and right direction as negative. 



Velocity of car B = -5 km/hr

Velocity of car C = + u km/hr

The relative velocity of car C w.r.t car B is,

     v = Velocity of car C - Velocity of car

        = u - (-5) = (u + 5) km/hr

Now the car C travels 5 km distance with relative velocity (u + 5) km/hr in 4 minutes.

Therefore, using the relation s = ut, we have

             5 equals left parenthesis straight u plus 30 right parenthesis cross times 4 over 60 

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rightwards double arrow        straight u space equals space 45 km divided by hr, is the speed of car C. 

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 scalar quantity?

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

Give three examples of scalar quantities.

Mass, temperature and energy

What is a vector quantity?

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