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Reshma swims back and forth in a 120 m long pool, covering a total distance of 240 m in 1 minute. What is her average velocity?
0 m/s
4 m/s
5 m/s
2 m/s
0 m/s
Whenever an object returns to its starting point in a closed-circuit movement (back and forth), the displacement is always 0, making average velocity 0 regardless of time taken.
Pool length = 120 m, Total distance = 240 m, Time taken = 1 minute = 60 seconds.
vavgтАЛ=╬Фt╬ФxтАЛ=txfinalтАЛтИТxinitialтАЛтАЛ
Whenever an object returns to its starting point in a closed-circuit movement (back and forth), the displacement is always 0, making average velocity 0 regardless of time taken.
Students often confuse 'Average Speed' (Total distance / Total time) with 'Average Velocity' (Total displacement / Total time).
Identify Displacement
Reshma swims from one end to the other (120 m) and returns to the starting point. Since she ends exactly where she began, the final position equals the initial position.
╬Фx=0┬аm
Define Average Velocity Formula
Average velocity is defined as the change in position (displacement) divided by the total time taken.
vavgтАЛ=╬Фt╬ФxтАЛ
Final Calculation
Substituting the displacement (0 m) and time (60 s) into the formula, we get the result.
vavgтАЛ=600тАЛ=0┬аm/s
A is correct because the total displacement of the swimmer is zero as she returns to her starting point, resulting in an average velocity of 0 m/s.
This concept frequently appears in Kinematics; always check if the motion is circular or back-and-forth, as these almost always yield zero displacement over full cycles.
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