Question

A glow worm of mass 4.8 g emits red light (650 nm) with a power of 0.10 W entirely in the backward direction. To what speed will it have accelerated after 10 yr if released into free space and assumed to live?

Answer 1

According to the question;

As we know that;

The energy of the single photon of frequency f orwave length lamda

So,
E = hc / lamda
So,

The glow warm emits energy 0.1 J persec
That is the number of photons emitted by the photon persec will be;

So,
n = 0.1 W / E
The numer of phtons emtted in 10 years,

Then,
N = n * 3.15*10^7 se/yr * 10 yr
Momentum associated with each photon
p= h / lamda

Then,
Momentum associated with N photon particles
P= N(h/lamda)   
Hence,

The change in the momentum of the glow is = NP in 10years,

So,
The Accelratrion of the glow,

a = NP/10yrs*(3.50^7 yrs /sec)