Question

A disc of diameter 0.4m and of mass 5kg is rotating about its axis at the rate of 28rev/sec. Find
1.angular momentum
2.rotational kinetic energy of disc

Answer 1

Answer:

Explanation:

Radius of ring , R = 0.4/2 = 0.2 m

mass of ring , M = 10 Kg

(i) moment of inertia , I = MR²

I = 10 × (0.2)²

= 10 × 0.04

= 0.4 Kg.m²

angular momentum , L = Iω

∵ ω = 2πν ,

here I = 0.4 Kg.m²

and ν = 2100rpm

= 1200/60 r/s

∴ L = 0.4 × 2π × 1200/60

= 50.24

= 51 Kgm²/s

(iii) Kinetic energy , K.E = 1/2Iω²

K.E = 0.4 × (2π × 1200/60)²/2

=3155.072 joule

Answer 2

Explanation:

Ans. 1. 0.586 kg M2 Ans. 2. 0.547 J