Correct option: (b) The magnitude of torque of the gravitational force on the particle about O is decreasing
Explanation:
If student will use angular momentum = mvr.
He/she may conclude answer (1) as r is decreasing angular momentum must decrease hence (1) is incorrect.
The magnitude of angular momentum of particle about O = mvd
Since speed v of particle increases, its angular momentum about O increases.
Magnitude of torque of gravitational force about O = mgd ⇒ constant
Moment of inertia of particle about O = mr2
Hence MI of particle about O decreases.
Angular velocity of particle about O = vsinθ
/ r
∴ v and sin θ increases and r decreases.
∴ angular velocity of particle about O increases.