Reference Frame Physics Example 3

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Example 3

medium
Car A travels north at 25 m/s25 \text{ m/s} and Car B travels south at 20 m/s20 \text{ m/s}, both relative to the ground. What is the velocity of Car A as seen by Car B?

Solution

  1. 1
    Define north as positive. vA=+25 m/sv_A = +25 \text{ m/s}, vB=−20 m/sv_B = -20 \text{ m/s}.
  2. 2
    Velocity of A relative to B: vAB=vA−vB=25−(−20)=45 m/s northv_{AB} = v_A - v_B = 25 - (-20) = 45 \text{ m/s north}

Answer

vAB=45 m/s northv_{AB} = 45 \text{ m/s north}
When two objects move in opposite directions, their relative speed is the sum of their individual speeds. A passenger in Car B sees Car A approaching at 45 m/s45 \text{ m/s}.

About Reference Frame

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

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More Reference Frame Examples

Example 1 easy

Train A moves east at [formula] and Train B moves east at [formula], both relative to the ground. Wh

Example 2 medium

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

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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