(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A flywheel has shape as a homogeneous cylinder with mass m = 40,0 kg and radius r = 0,50 meters. The cylinder is rotating round the axis of symmetry, and is runned by a motor with constant angular velocity (w0). When the motor is switched off, the cylinder is affected by a moment of force that are caused by friction.

How long will the cylinder rotate before the angular velocity is halved?

2. Relevant equations

The friction: M = -kw

w = omega

k = (1,2 * 10^2) Nm/s

3. The attempt at a solution

The moment of inertia: I = (m*r^2)/2 (cylinder)

M = -kw => 1) w = -(M/k)

w = 1/2*w0

alpha = w/T = (1/2*w0)/T

1) (1/2*w0) = -(M/k)

(1/2*w0) = -((I*alpha)/k)

(1/2*w0) = -((((m*r^2)/2)*((1/2*w0)/T))/k)

When solving this equation the answer is: T = -416

BUT sadly we are quite sure this answer is incorrect, any help will be appreciated.

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Rotating cylinder, how long will it take before the angular velocity is halved

**Physics Forums | Science Articles, Homework Help, Discussion**