Question

A circular disc has a mass of 1 kg and radius 40 cm

Answer 1

Mass, M = 1 kg

Radius, R = 40 cm = 0.4 m

Revolution per second = 10 rev/s

Angular velocity, ω = 2×π×10 = 62.8 rad/s

So, KE = ½ I ω2 = ½ (½ MR2)ω2

=> KE = ¼ × 1 × 0.42 × 62.82 = 157.75 J

Final kinetic energy is = 0, because the disc stops rotating.

So, work done to stop the disc is = 157.75 – 0 = 157.75 J ≈ 158 J

Answer 2

Mass, M = 1 kg

Radius, R = 40 cm = 0.4 m

Revolution per second = 10 rev/s

Angular velocity, ω = 2×π×10 = 62.8 rad/s

So, KE = ½ I ω2 = ½ (½ MR2)ω2

=> KE = ¼ × 1 × 0.42 × 62.82 = 157.75 J

Final kinetic energy is = 0, because the disc stops rotating.

So, work done to stop the disc is = 157.75 – 0 = 157.75 J ≈ 158 J