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  • An object is kept at 40 cm from a concave mirroe of focal length 20 cm. If the object start moving along perpendicular to principle axis with 6 cm/s then velocity of image is :<div class='qna-o

An object is kept at 40 cm from a concave mirroe of focal length 20 cm. If the object start moving along perpendicular to principle axis with 6 cm/s then velocity of image is :

Option: 1

3 cm/s


Option: 2

4 cm/s


Option: 3

6 cm/s


Option: 4

8 cm/s


Answers (1)

best_answer

As we learn

If object is moving perpendicular to the principal axis -

\frac{dh_{2}}{dt}= -\frac{v}{u}.\frac{dh_{1}}{dt}
 

- wherein

\frac{dh_{1}}{dt}= velocity of object perpendicular to the principal axis.

 

\frac{dh_{2}}{dt}= velocity of image perpendicular to the principal axis.

 

 

u = -40 cm , f = -20 cm

\Rightarrow \frac{1}{v}=\frac{1}{f}-\frac{1}{u}= -\frac{1}{20}+\frac{1}{40}=-\frac{1}{40}

V= -40 cm

\frac{dh_{2}}{dt}= - \frac{u}{v} . \frac{dh_{1}}{dt}=-\frac{-40}{-40}.6 cm/s

 

\frac{dh_{2}}{dt}= - 6 cm/s

 

Posted by

avinash.dongre

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