When an object is kept at a distance of 30cm from a concave mirror, the image is formed at a distance of 10 cm. If the object is moved with a speed of `9cm s^(-1)` the speed with which the image moves is

Answer

1

Explanation

` (1)/(u) + (1)/(v) = (1)/(f)`
`- (du)/( u^(2)) - (dv)/(v^(2)) = 0 or - (dv)/( v^(2)) = (du)/( u^(2))`
or `dv = - (v^(2))/( u^(2)) du`
`= - (10 xx 10)/( 30 xx 20) xx 9 ms^(-1) = - 1ms^(-1)`