Important Question

Rest and Motion are relative terms . Why?
Rest and motion are relative terms because if we suppose a tree on the roadside.It is the state of rest as it is not changing its position with respect to a moving car but a car changes it position with respect to the tree. As,it is the state of motion, Therefore the treee is at rest but the running car is in motion relative to the tree. Hence rest and motion are relative terms.

Difference Between

Difference between scalar and vector quantity

Scalar	Vector
The quantities that have magnitude but no direction is called scalar quantity.	The quantities that have both magnitude and direction is called scalar quantity.
It is denoted by ‘A’	It is   represented by arrow head  with
It is measured by certain degebric matter.	It is added by certain vactor rule.
Sum of scalar quantity is always positive	Sum of scalar quantity can be positive, negative or zero

Relative motion

Relative motion
Motion of a body is described in the terms of motion of another body is called relative motion


Relative velocity
The relative velocity is defined as the velocity of the body with respect to another body 
                            "OR"
It is also defined as a distance between of two bodies.


There are three cases of relative motion . They are:-


Case 1
When in opposite  direction

V_AB = Relative velocity 

               timetaken

         = 75 km + 90 km 

                      1hr

         = 165 km/hr

Conclusion

V_AB = V_A+V_B

Case 2

When in same direction

V_AB = 100-80

               1   

        = 20 km/hr

Conclusion

V_AB = V_A-V_B

V_AB = V_B-V_A

Case 3

If two bodies are moving uniformly i.e. they are moving in the same direction with same velocity then the relative velocity = 0

  

Acceleration

Acceleration

The rate of change per unit time is called acceleration.It is a vector quantity and it is denoted by "a".In SI System unit of a acceleration is m/s².

Initial Velocity= u
Final velocity  = v
Time taken      = t
Acceleration    = Final velocity - initial velocity
                                        Time taken
                          = v-u
                               t
Note*


# If a body starts from rest to motion u= 0

# If a body suddenly stops due to the application                               of external force, like- by applying brakes, v=0

# If a body is thrown vertically upward, at maximum height, v = 0