Image of an object approaching a convex mirror of radius of curvature 20m slong its optical axis is observed to move from `(25)/(3)`m to `(50)/(7)`m in 30 seconds. What is the speed of the object in km per hour?

Answer

`3Km//h`

Explanation

`R=20cm,f=10cm`
Formirror
`(1)/(V)+(1)/(U)=(1)/(f) rArr (1)/(25//3)+(1)/(U_(1))=(1)/(10)`
`(1)/(U_(1))=(1)/(10)-(3)/(25)=-(1)/(50)rArr U_(1)=-50cm`
and`(1)/(50//7)+(1)/(U_(2))=(1)/(10) rArr(1)/(U_(2))=-(1)/(25) rArrU_(2)=-25cm`
So,speed=`|(DeltaU)/(Deltat)|=(25)/(30)m//sec` and in `km//hrs=(5)/(6)xx(18)/(5)=3km//hr`
`3km//hr`