IIT JEE , AIEEE Forum - Physics , Optics

Mr.IITIAN007

Check this out!!!!!!!!!!!!!!!
A particle is moving at a constant speed v from a large distance towards a convex mirror of radius R along its principal axis . Then try to find out the speed of the image formed by the mirror as a function of the distance x of the particle from the
mirror.In fact a same type of question is there in H.C.VERMA.

karthik2007

Lemme have a go :

Let the distance of the particle from the mirror be x. We are given dx/dt = v.

If v is the image distance, we've got to find dv/dt.

Now, since we are given R, using lens maker's formula,. we can get f :

1/f = (1-M)(2/R) (M for glass is 1.5)

Now, Using mirror formula, 1/v-1/u=1/f, and differentiating both sides with respect to time, (here f is a constant), You should get the required result.

Am I right or what?

phyana

hai guys .....................the speed of the image wrt the mirror is also v..........but wrt object the ans is 2v
need not differentiate................use numbers to get it

karthik2007

Phyana, you are wrong. The speed of the image is not v. V is the distance of the image from the principal focus.

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