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posted by  SaV33AgE on 10/5/2008 2:01:24 AM  |  status: Closed  

vector question, need help

Course Textbook Chapter Problem
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Question Details:
two vectors lie with their tails at the same point. when the angle between them increase by 20 degree their scalar product has the same magnitude but change from postive to negative. the orginal angle between them was
 
a) 60
b) 70
c) 80
d) 90
e) 0
 
 
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posted by EngAve on 10/5/2008 2:04:13 AM  |  status: Live
Asker's Rating: Helpful   
SaV33AgE's comment:
"would be nice to know y 80..90 could be a valid answer is it not?"
Response Details:
c.) 80°
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posted by Solomon08 on 10/5/2008 2:10:03 AM  |  status: Live
Asker's Rating: Lifesaver   
SaV33AgE's comment:
"thanks.."
Response Details:
c) 80
 
 
 in scalar product  we have cos of the angle .cos will be negetive only if the angle is in between  90 and 270 . in the given options , 80 is the only angle with which we get more than 90 by adding 20 degrees

 
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