Question

A disc of diameter 0.4m and of mass 10 kg is rotating about its axis at the rate of 1200 rev\ min find the angular momentum and rotational kinetic energy of the disc

Answer 1

When diameter is 0.4 then radius is 0.2

When you apply the formula o angular momentum i.e 2pie *r divided by T then the ans is 25.143rad/sec

The kinetic energy is given by 1/2 (mv^2) which is 126.434joule if ans come to be correct than remember me

Answer 2

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