NEET 2020 Model Question Paper 4

As the system is initially at rest, therefore, initial angular momentum
Li=0.
According to the principle of conservation of angular momentum, final angular momentum, Lf=0.
∴ Angular momentum of disc = Angular momentum of man is in opposite direction of platform.
i.e., mvR=Iω
or ω=

mvR

I

=

50×1×2

200

=

1

2

‌rad‌s−1
Angular velocity of man relative to platform is
or ωr=ω+

υ

R

=

1

2

+

1

2

=1‌rad‌s−1
Time taken by the man to complete one revolution is T=

2π

ωr

=

2π

1

=2πs