Question

please explain this question

Answer 1

This is the question related to conservation of angular momentum.

Metallic circular wheel of mass M. Let us take it as a Ring or disc.
Initial Radius = R1    
Final radius = R2. = R1 + 0.2/100 R1 =  R1* 1.02
Let k be a constant.

Moment of inertia = I1 = k * M R1²  , initial
                             = I2 = k M R2²  ,  final

Let us say initial angular velocity = ω1.
   Final angular velocity is = ω2.

So Ang. Momentum = I1 * ω1 = I2 * ω2
 So   ω2/ω1 = I1 /I2 = R1²/R2² = 1/1.02² ≈ 1 - 0.04
         ω2 / ω1 ≈ 0.96

Answer is (4) decreases by 0.04 %

Answer 2

this is related to conservation of angular momentum