Question

A plane mirror is approaching you at a speed of $10cm/sec$You can see your image in it. At what speed will your image approach you

• A. $10cm/sec$
• B. $5cm/sec$
• C. $20cm/sec$
• D. $15cm/sec$

Answer 1

Answer: (C)

$20cm/sec$

Answer 2

Suppose at any instant, plane mirror lies at a distance x from object. Image will be formed behind the mirror at the same distance x.

When the mirror shifts towards the object by distance ‘y’ the image shifts $= x + y - (x - y) = 2y$

So speed of image = 2 × speed of mirror