According to the law of conservation of momentum, momentum lost by photons = momentum gained by glow-worm Momentum lost by photons = no of photons x momentum lost by one photon =‌
‌ Totalenergy ‌
‌ energy of ‌‌ photon‌
×‌
h
λ
[ Debroglie' equation λ=‌
h
p
⋅p=‌
h
λ
] =‌
‌ power ‌x‌ time ‌
hc
λ
×‌
h
λ
=‌
0.1×365×24×60×60×10
3×108
⇒(1) Momentum gained by glow-worm =‌
5
1000
×(v) in m∕sec⟶(2)(1)=(2) Hence v=21 msec Ans. ‌