Question

When a person is moving in front of plane mirror then what is the speed of person in mirror?

Answer 1

When a person is moving in front of a plane mirror then his speed is equal to his image speed.

The distance traveled by the man is equal to the distance traveled by his image in the mirror.
Similarly the time taken to travel this distance is also equal.

So the speed of the man and his image in the mirror is also equal.

Hope This Helps You!

Answer 2

we know in plane mirror,
       distance of object from mirror=distance of image from mirror
e.g.  dist. of object wrt mirror = dist. of image wrt mirror 
         
Let dist. of object wrt mirror = $D_{om}$
dist. of image wrt mirror =$D_{im}$

$D_{om} = D_{im}$
differentiate wrt time 
$V_{om}= V_{im}$

  it means speed  of object with respect to mirror is equal to speed of image with respect to mirror .
by using sign ,
   $V_{om} =- V_{im} \\ V_o - V_m = -(V_i - V_m) \\ V_o + V_i = 2V_m$
here plane mirror is in rest .so,$V_m = 0$
hence , 
$V_o =- V_i$

it means speed of person in mirror is equal speed of image of the person but in opposite direction