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Relative Velocity Formula

Last updated date: 24th Feb 2024
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Relative Velocity Equation

Relative velocity is used to designate the aircraft traveling in the wind or boats sailing through the water, etc. The velocity is calculated within the object as per the observer using the relative velocity formula in relativity. It can be computed with the help of an intermediate reference frame. Simply, this can be the vector sum of the velocities. The formula to find relative velocity is expressed as:

vAB = vA – vB.


VAB = the velocity in reference to A and B, 

VB = the velocity with reference to B 

VA = is the velocity in reference to A 

Solved Examples Using Dimensional Formula of Relative Velocity


A bus with a speed of 90 m/s with respect to the ground in the west direction. An onlooker is moving at a speed of -25m/s with respect to the train in the west direction. Find out the speed of the onlooker with respect to the ground?


From the problem, it is familiar that,

VAB (Velocity of man in reference to train) = -25m/s

VB (Velocity of train in reference to ground) = 90 m/s

VA (Velocity of an onlooker in reference to ground) =?

Relative Velocity Formula is,

vAB = vA – vB.

vAB→ = -25 - 90 = -115m/s

Thus, VAC→ = -115m/s

FAQs on Relative Velocity Formula

1. What is Relative Velocity?

Answer: Seeing that we and our co-passengers are traveling together, thus, there is no relative velocity between us and the passengers. In addition, the trees are stationary while we are moving. Therefore, the trees are moving at a certain relative velocity in reference to us and the other passengers. Here, the relative velocity is the variance of velocities between you and the tree.

Relative velocity is usually incorporated to define the motion of airplanes in the wind or moving boats across water etc. This velocity is measured as per the person as an onlooker inside the object. This can be identified by introducing an intermediate framework of reference.

2. What is the Difference Between Velocity and Relative Velocity?

Answer: The comparison between velocity and relative velocity is that velocity is computed in reference to a reference point that is relative to a different point. While relative velocity is calculated in a frame where an object is either moving or at rest in reference to the absolute frame.

3. State If the Following Statement is True or False: Relative Velocity May Also Be Negative.

Answer: The statement is true that the relative velocity can be negative. As relative velocity is the variance between two velocities regardless of the magnitude of the velocities, it can be negative.