A car is fitted with a convex side-view mirror of focal length 20 cm . A second car 2.8 m behind the first car is overtaking the first car at relative - Physics MCQ FIITJEE AIEEE 2011 (Set Q) 2026 | ExamTest.live

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A car is fitted with a convex side-view mirror of focal length 20 cm . A second car 2.8 m behind the first car is overtaking the first car at relative speed of 15 m/s . The speed of the image of the second car as seen in the mirror of the first one is:

Solution & Step-by-step Explanation

Mirror formula: \frac{1}{v} + \frac{1}{u} = \frac{1}{f} .Differentiating with respect to time: - \frac{1}{v ^{2}} \frac{d v}{d t} - \frac{1}{u ^{2}} \frac{d u}{d t} = 0 ⟹ v_{i} = - (\frac{v}{u})^{2} v_{o} Given f = 20 cm = 0.2 m, u = - 2.8 m . \frac{1}{v} = \frac{1}{0.2} - \frac{1}{- 2.8} = 5 + \frac{1}{2.8} = \frac{14 + 1}{2.8} = \frac{15}{2.8} v = \frac{2.8}{15} m Speed of image = (\frac{v}{u})^{2} v_{o} = (\frac{2.8/15}{2.8})^{2} \times 15 = (\frac{1}{15})^{2} \times 15 = \frac{1}{15} m/s

Try it yourself before checking the explanation above.

A car is fitted with a convex side-view mirror of focal length 20 cm . A second car 2.8 m behind the first car is overtaking the first car at relative speed of 15 m/s . The speed of the image of the second car as seen in the mirror of the first one is:

\frac{1}{15} m/s

10 m/s

15 m/s

\frac{1}{10} m/s

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