Thursday
February 11, 2016

# Homework Help: Physics

Posted by Lauren on Sunday, July 29, 2012 at 6:28pm.

A spinning disk of mass 5.0 kg and radius 0.25m is rotating about an axis through its center at 400 rev/min.
a.) What is the angular velocity of the disk in rad/s?
b.) What is the moment of inertia of the disk?
c.) If it accelerates at a constant rate to 800 rev/min in 8 sec, what is its angular acceleration?
d.) What constant torque is required to produce this acceleration?
e.) When it reaches that speed, what is its kinetic energy?
f.) When it reaches that speed, what is its angular momentum?
• Physics - drwls, Sunday, July 29, 2012 at 6:40pm

a) Convert revolutions per minute to radians per second. Surely you can do that.

b) The moment of inertia of a disc of radius R and mass M is
I = (1/2)M*R^2

c) Convert 800 rev/min to
w = ___ radians/sec, and divide that by 8.0 seconds for the angular acceleration, ____rad/s^2.

d) Torque = (Moment of inertia)*(angular accleration)

e) (1/2) I w^2

f) I*w

You do the numbers.