ncert class XII page 316....chapter 9 example 9.4
havin a doubt in this example.....when i solve it by differentiating th mirror equation wrt time....m getting an answer different from the achieved by the method shown here....
mmm........is the method if differentiating incorrect???
and if so...why??
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3 Answers
1it can b don with diff ....but chek wether u r applying it ritely.....show ur calc
1on differentiating the mirror equation,
-1/v^2 dv/dt - 1/u^2 du/dt = 0
At u = -39 m
1/v - 1/39 =1
then, v = 39/40 m
so -dvdt * 1(3940)^2 - 5 *(1-39)^2 = 0
and then on solving i getdv/dt= -1/320 m/s
for 29 m, i get -1/180 m/s
for 19 m, -1/80 m/s
and for -9m, -1/20m/s....
none of the answer matches...
39I tried your method, cat...I am also getting your values. I don't know why it's different from those in the book...
Differentiating mirror formula gives instantaneous velocities of object and image, but by applying values of u and v we should get the right ans.