Reference Frame Physics Example 1

Follow the full solution, then compare it with the other examples linked below.

Example 1

easy
Train A moves east at 30 m/s30 \text{ m/s} and Train B moves east at 20 m/s20 \text{ m/s}, both relative to the ground. What is the velocity of Train A relative to Train B?

Solution

  1. 1
    The velocity of A relative to B is: vAB=vA−vBv_{AB} = v_A - v_B.
  2. 2
    vAB=30−20=10 m/s eastv_{AB} = 30 - 20 = 10 \text{ m/s east}
  3. 3
    From the perspective of a passenger on Train B, Train A appears to move east at 10 m/s10 \text{ m/s}.

Answer

vAB=10 m/s eastv_{AB} = 10 \text{ m/s east}
A reference frame is a viewpoint from which motion is observed. Relative velocity between two objects is found by subtracting their velocities. Different observers can measure different velocities for the same object.

About Reference Frame

A coordinate system attached to a particular observer that is used to describe the positions and motions of objects.

Learn more about Reference Frame →

More Reference Frame Examples

Example 2 medium

A boat travels at [formula] relative to the water, heading directly across a river that flows at [fo

Example 3 medium

Car A travels north at [formula] and Car B travels south at [formula], both relative to the ground.

Example 4 hard

A plane flies at [formula] due north relative to the air. A wind blows at [formula] from the west (t

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