Question

David stands 2.5 meters in front of a plane mirror.

A) How far from David is David’s image in the mirror?

B)If David moves away from the mirror at 1.5 m/s, how fast are David and his image moving apart from each other?

C) If David is 180cn tall, how tall is his image in the mirror?

Please explain

Answer 1

David stands at 2.5 m infront of a plane mirrror

A )

the image distanceof the David in the mirror is  

we know that the relation between object distance and image distance for plane mirror is  

s = -s'

s object distance , s' is image distance -ve sign is virtual image

so the David image will be formed at 2.5 m behind the mirror

B)

if David moves away from the mirror at 1.5 m/s,

the image will also moves away from each other.

C)

we know that linear magnification is m = -s'/s

for plane mirror , s = -s' so m = -(-s')/s = s'/s = 1

so if the Davis is 180 cm tall then the image also same size 180 cm

because m = 1