Question

If a solid sphere of mass 200g and radius 20cm is rotating with an angular velocity of 5 rad s^-1, its rotational kinetic energy is _____

(a) 0.06J

(b) 0.04J

(c) 0.03J

(d) 0.004J

This question was addressed to me in exam.

This intriguing question originated from Kinetic Energy in portion Work, Energy and Power of Physics – Class 11

Answer 1

Right option is (b) 0.04J

The explanation is: Rotational kinetic energy is given by 0.5*I*Ω^2. I of a solid sphere is given by (2/5)*m*r². So, rotational kinetic energy is 0.5*0.4*(200/1000)*(20/100)^2*5^2 = 0.04J.