An object is placed in front of a convex mirror-at a distance of 60m from its pole- Object starts moving towards the mirror at 20 m-s-Find the average velocity of the image for a time interval of 2 sec if the-focal length of the mirror is 20m-20 m-s-10 m-s-30 m-s-None of the above-

The correct option is D None of the above 1/v + 1/u = 1/f 1/v 1/ 60 = 1/20 1/v 1/60 = 1/20 v = 15 m Now as object moves at 20 m/s , in two seconds it rea ...

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Standard VIII

Physics

Mirror Formula

An object is ...

Question

An object is placed in front of a convex mirror at a distance of 60m from its pole. Object starts moving towards the mirror at 20 $\frac{m}{s}$ . Find the average velocity of the image for a time interval of 2 sec if the focal length of the mirror is 20m.

20 m/s

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10 m/s

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30 m/s

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None of the above

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Solution

The correct option is D
None of the above

$\frac{1}{v}$ + $\frac{1}{u}$ = $\frac{1}{f}$

$\frac{1}{v}$ - $\frac{1}{- 60}$ = $\frac{- 1}{20}$

$\frac{1}{v}$ - $\frac{1}{60}$ = $\frac{1}{20}$

v = 15 m

Now as object moves at 20 $\frac{m}{s}$ , in two seconds it reaches u = -20m

$\frac{1}{v}$ + $\frac{1}{- 20}$ = $\frac{1}{20}$

$\frac{1}{u}$ = $\frac{1}{20}$ + $\frac{1}{20}$

u = 10 m
Now average speed of the image is given by = $\frac{15 - 10}{2}$
= 2.5 $\frac{m}{s}$

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An object is placed in front of a convex mirror at a distance of 60m from its pole. Object starts moving towards the mirror at 20 ms. Find the average velocity of the image for a time interval of 2 sec if the focal length of the mirror is 20m.

The correct option is D None of the above 1v + 1u = 1f 1v - 1−60 = −120 1v - 160 = 120 v = 15 m Now as object moves at 20 ms , in two seconds it reaches u = -20m 1v + 1−20 = 120 1u = 120 + 120 u = 10 m Now average speed of the image is given by = 15−102 = 2.5 ms

An object is placed in front of a convex mirror at a distance of 60m from its pole. Object starts moving towards the mirror at 20 $\frac{m}{s}$ . Find the average velocity of the image for a time interval of 2 sec if the focal length of the mirror is 20m.