Relative Velocity
Two cars on a straight highway move in the same direction at 25 m/s and 15 m/s respectively, what is the velocity of the faster car relative to the slower car?
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About This Question
- Subject
- physics
- Chapter
- kinematics
- Topic
- relative velocity
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
10m/s
As outlined in NCERT Class 11, Chapter 3 (Motion in a Straight Line), the relative velocity of one object with respect to another moving along the same line is the vector difference of their velocities. When both move in the same direction, the relative velocity magnitude is the simple difference of their speeds. Taking the direction of motion as positive, the faster car's velocity relative to the slower car is 25 − 15 = 10 m/s. The option 40 m/s is wrong because it adds the speeds, which applies only when objects move in opposite directions. The option 5 m/s arises from an arithmetic slip in subtraction. The option 20 m/s incorrectly averages the two speeds rather than taking their difference. Plausibility check: an observer in the slower car would see the faster car pulling ahead slowly, gaining 10 m every second, which matches everyday highway experience and confirms that 10 m/s is the physically sensible relative velocity.
This easy difficulty physics question is from the chapter kinematics, covering the topic of relative velocity. It appeared in the 2025 exam.
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