The Best Answer for the moment of inertia.

If the side length is 40 cm, then the height is

h = 40cm * √3/2 = 34.6 cm

(from years of looking at equilateral triangles)

The center is 1/3 of the way up the height, so the top is

r = (2/3)*34.6cm = 23 cm

away from the center. That means that all three corners are 23 cm from the center.

Then I = 3mr² = 3 * 0.21kg * (0.23m)² = 0.033 kg·m²

5.2rev/s * 2πrad/rev = 32.7 rad/s, so

KE = ½Iω² = ½ * 0.033kg·m² * (32.7rad/s)² = 18 J

Lorem ipsum dolor sit amet, consectetur adipiscing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam,
quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor
in reprehenderit in voluptate velit esse cillum dolore eu fugiat.

SHOW ANSWER