angular acceleration problem

by Punchlinegirl
Tags: acceleration, angular
Punchlinegirl is offline
Nov6-05, 08:47 PM
P: 225
A rod of length 57.0 cm and mass 1.90 kg is suspended by two strings which are 41.0 cm long, one at each end of the rod. The string on side B is cut. Find the magnitude of the initial acceleration of end B.

I tried using torque= I* alpha
torque= L x f= (.57)(18.62)=10.6
I got from Newton's 2nd law, (9.8)(1.90)
so, 10.6 = I* alpha
I= (1/12)(mL^2)= (1/12)(1.90 * (.57)^2= .051
so, 10.6 = .051 alpha
alpha = 207.8 rad/s^2
alpha= a/L
207.8 = a / .57
a= 118.4 m/s ^2

This isn't right... can someone please help me?
Phys.Org News Partner Science news on
Internet co-creator Cerf debunks 'myth' that US runs it
Astronomical forensics uncover planetary disks in Hubble archive
Solar-powered two-seat Sunseeker airplane has progress report
lightgrav is offline
Nov6-05, 09:00 PM
HW Helper
PF Gold
lightgrav's Avatar
P: 1,125
First, the place that it is rotating around is at one end of the rod.
How far from this is the rod's center-of-mass?

Newton's 2nd law is "Sum of Forces = ma"
Maybe you mean Newton's 4th Law "Force by gravity = m g = m GM/r^2"

Register to reply

Related Discussions
angular acceleration problem Introductory Physics Homework 1
Another Angular Acceleration Problem Introductory Physics Homework 4
Angular Acceleration problem... Introductory Physics Homework 2
angular acceleration problem Introductory Physics Homework 9