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.
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:
Distance travelled by the object is the product of speed and time.
Therefore, now the object distance:
Applying mirror formula to find the final position of the image vf:
Average speed is the ratio of total distance travelled to the total time taken.
Average speed of the image: