Go Back   Physics Help Forum > Physics Forums > Physics

Physics Physics Forum - General Physics Discussion and Physics News

Like Tree2Likes
  • 1 Post By ChipB
  • 1 Post By Pmb
Reply
 
LinkBack Thread Tools Display Modes
Old Nov 8th 2018, 01:06 AM   #1
Junior Member
 
Join Date: Nov 2018
Posts: 1
A question regarding vectors and angle between vectors

In my attempt, I got 2 answers √3 and 1 but the solutions say that the answer is only √3. Am I missing something?

Sent from my S6 using Tapatalk
raazdeep is offline   Reply With Quote
Old Nov 9th 2018, 05:45 AM   #2
Physics Team
 
ChipB's Avatar
 
Join Date: Jun 2010
Location: Morristown, NJ USA
Posts: 2,320
Consider the first equation you are given:

$ | \hat A \times \hat B | = - \sqrt 3 \ \hat A \cdot \hat B $

The left hand side is a positive number, since it's a magnitude. Therefore the right hand side must also be positive, which means $ \hat A \cdot \hat B$ must be negative. This rules out the possibility that theta = -60 degrees.
topsquark likes this.
ChipB is offline   Reply With Quote
Old Yesterday, 02:30 PM   #3
Pmb
Physics Team
 
Join Date: Apr 2009
Location: Boston's North Shore
Posts: 1,569
Originally Posted by ChipB View Post
Consider the first equation you are given:

$ | \hat A \times \hat B | = - \sqrt 3 \ \hat A \cdot \hat B $
That expression is not in the paper he posted. The cross product is defined for two vectors whose magnitude does not appear explicitly in the expression defining it;.
topsquark likes this.
Pmb is offline   Reply With Quote
Old Yesterday, 03:59 PM   #4
Physics Team
 
ChipB's Avatar
 
Join Date: Jun 2010
Location: Morristown, NJ USA
Posts: 2,320
Originally Posted by Pmb View Post
That expression is not in the paper he posted.
?? It’s the very first line of the photo the OP posted from his text with the problem statement - are you not seeing it?

Last edited by ChipB; Yesterday at 04:02 PM.
ChipB is offline   Reply With Quote
Reply

  Physics Help Forum > Physics Forums > Physics

Tags
angle, question, vectors



Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Vectors help! again princess44725 Kinematics and Dynamics 2 Jun 29th 2012 09:00 PM
vectors Sterlingm Kinematics and Dynamics 1 Jun 27th 2010 01:20 PM
Vectors decoy808 Kinematics and Dynamics 2 Nov 24th 2009 06:17 PM
Quick Relative motion with Vectors Question! KaylaN Kinematics and Dynamics 2 Sep 22nd 2009 09:31 AM
Question on vectors Ralph4christ Kinematics and Dynamics 7 May 31st 2009 11:43 AM


Facebook Twitter Google+ RSS Feed