    Question

# An object is placed in front of a convex mirror at a distance of 60 m from its pole. Object starts moving towards the mirror at 20 ms−1. Find the average speed of the image for a time interval of 2 s if the focal length of the mirror is 20 m.

A

0.568 ms1

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B

1 ms1

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C

3 ms1

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D

2.5 ms1

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Solution

## The correct option is D 2.5 ms−1 Given: Initial object distance, u=−60 m Speed of object, vo=20 ms−1 Focal length, f=20 m Time interval, t=2 s Applying mirror formula to find the initial position of the image v: 1v+1u=1f 1v+1−60=120 v=15 m Distance travelled by the object is the product of speed and time. so=vot so=20×2=40 m Therefore, now the object distance: uf=u+so=−60+40=−20 m Applying mirror formula to find the final position of the image vf: 1vf+1uf=1f 1vf+1−20=120 vf=10 m Average speed is the ratio of total distance travelled to the total time taken. Average speed of the image: vi=v−vft vi=15−102=2.5 ms−1  Suggest Corrections  2      Similar questions  Related Videos   Image formation in convex mirrors Tackle
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