# Rotational inertia and kinetic energy of spinning blades

A helicopter has 3 blades, each of them are 5.20m long and has a mass of 220kg.(each blade has a mass of 220kg, not the sum of the 3) The rotor is rotating at 385 rev/min.

a)What is the rotational inertia of the rotor assembly about the axis of rotation? (Each blade can be considered to be a thin rod rotated about one

end.) ____kg*m^2

b)What is the total kinetic energy of rotation?___MJ

Â© BrainMass Inc. brainmass.com February 24, 2021, 2:22 pm ad1c9bdddfhttps://brainmass.com/physics/rotation/rotational-inertia-and-kinetic-energy-of-spinning-blades-17091

#### Solution Preview

The rotational interia of an object, such as a helicopter blade, is a measure of that object's resistance to angular accelerations -- it serves the same function as mass in the rotational analogue of Newton's law (F = ma for linear motion, F = TI for rotational motion).

<br>

<br>Rotational ...

#### Solution Summary

This solution contains a brief step-by-step guide to calculate the rotational inertia and kinetic energy. The formula for the rotational inertia of a rigid rod is stated but not derived.