JEE Advanced 2020 Concept Recapitulation Test 4 Paper 2

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. ‌

v

7

=3.