question_answer

A plane mirror is approaching you at a speed of \[10\,cm/sec\]You can see your image in it. At what speed will your image approach you                                                                  [CPMT 1974]

A)            \[10cm/sec\]                       

B)            \[5cm/sec\]

C)            \[20cm/sec\]                       

D)            \[15cm/sec\]

Correct Answer: C

Solution :

                   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