**JEE Advanced 2019 Paper 2, Question 12**

A perfectly reflecting mirror of mass mounted on a spring constitutes a spring-mass system of angular frequency such that with as Planck’s constant. photons of wavelength strike the mirror simultaneously at normal incidence such that the mirror gets displaced by .

If the value of is , what is the value of ?

[Consider the spring as massless]

**Solution**

The momentum carried by a single photon is given by the de Broglie relation . The total momentum carried by photons is therefore . All the photons hit the mirror simultaneously and are reflected …