InterviewSolution
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InterviewSolution
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An object is present on the principal axis of a concave mirror at a distance 30cm from it. Focal length of mirror is 20cm. Q. If object starts moving with `2cms^(-1)` along principal axis towards the mirror then,A. image starts moving with `4cms^(-1)` away from the mirrorB. image starts moving with `4cms^(-1)` towards the mirrorC. image starts moving with `8ms^(-1)` towards the mirrorD. image starts moving with `8cms^(-1)` away from the mirror |
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Answer» Correct Answer - d. Let `u=-x, v=-y` `(dx)/(dt)=-2cms^(-1),(1)/(-y)+(1)/(-x)=(1)/(f)` `rArr (1)/(y^(2))(dy)/(dt)+(1)/(x^(2))(dx)/(dt)=0` `rArr (dy)/(dt)=-((y)/(x))^(2)(dx)/(dt)rArrv_(I)=-((60)/(30))^(2)(-2)=8cms^(-1)` |
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