Relative velocity

-For two objects A and B moving with the uniform velocities VA and VB.
Relative velocity is defined as
VBA=VB-VA
where VBA is relative velocity of B relative to A

Similiary relative velocity of A relative to B
VAB=VA-VB
Special cases.
For straight line motion,we can just add or subtract to get the relative velocity.
If the objects are moving in the same direction,relative velocity can be get by substracting other.If they are moving in opposite direction ,relative velocity will be get by adding the velocities example like train problems

For two dimensions motion,we will need to add or subtracting components along x & y direction to get the relative velocity
Suppose
vA=vxai + vyaj
vB=vxbi + vybj

Relative velocity of B relative to A
=vxbi + vybj -(vxai + vyaj)
=i(vxb-vxa) + j(vyb-vya)

For three dimensions motion
vA=vxai + vyaj +vzaz
vB=vxbi + vybj + vzbz

Relative velocity of B relative to A
=vxbi + vybj + vzbz -(vxai + vyaj +vzaz)
=i(vxb-vxa) + j(vyb-vya)+z(vyb-vya)

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