An object AB of height 1cm lying on the axis of convex mirror of focal length20cm, at a distance of 30cm from its pole as shown in figure. Now the object starts moving with a constant speed `1 cm//sec` towards the pole. Calculate Q. Magnitude of velocity of image at the given instantA. `0.08cms^(-1)`B. `0.64cms^(-1)`C. `0.16cms^(-1)`D. `0.32cms^(-1)`

An object AB of height 1cm lying on the axis of convex mirror of focal

1.	An object AB of height 1cm lying on the axis of convex mirror of focal length20cm, at a distance of 30cm from its pole as shown in figure. Now the object starts moving with a constant speed `1 cm//sec` towards the pole. Calculate Q. Magnitude of velocity of image at the given instantA. `0.08cms^(-1)`B. `0.64cms^(-1)`C. `0.16cms^(-1)`D. `0.32cms^(-1)`
Answer» Correct Answer - c. (i) Given : `u=-30cm, f=20cm` `(1)/(v)+(1)/(u)=(1)/(f)rArrv=12cm` Also, `(dv)/(dt)=-((v^(2))/(u^(2)))(du)/(dt)=-0.16cms^(-1)` (ii) `H=-(v)/(u)h`, H is the height of image and h is height of object. `(dH)/(dt)=(u(dv)/(dt)-v(du)/(dt))/(u^(2))h=0.008cms^(-1)`

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