Question

please answer correctly. question no. 2.

Answer 1

M = +1/5  or -1/5 and  v = +18 cm  or -18 cm

So there are 4 possibilities.But v positive means behind convex mirror and hence, the image has to be erect.  Hence,m is positive only.There are 3 cases only.

It is a mirror:     m = -v/u               1/f = 1/v + 1/u

case i)
  m = +1/5  = -v/u      let v = +18 cm   
     u = - 5 v = -90 cm
    1/f = 1/18 - 1/90 = 4/90  =>  f = +22.5 cm
 It is a Convex Mirror.

case ii)
   m = +1/5 = -v/u   let  v = -18 cm
       u =  +90 cm      
Not possible as u is always negative.

case iii)
   m = -1/5 = -v/u       let v = +18 cm
   u  = +90 cm    
Not possible.

case iv)
    m = -1/5    = -v/u        u = 5 v
   v = -18 cm  
   1/f = -1/18 - 1/90 = -6/90
     f = -15 cm      
It is a concave mirror.

HOPE IT HELPS!!