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  #11  
Old Sunday, May 24, 2015
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A rod lies parallel to the x-axis of reference frame S, moving along this axis at a speed of 0.632 C. Its rest length is 1.68m. What will be its measured length in frame S?




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  #12  
Old Sunday, May 24, 2015
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Three vectors are given by:
a = 3i + 3j -2k
b = -i - 4j + 2k
c = 2i + 2j – k
Find (i) a. (b. × c), (ii) a. (b. + c), (iii) a. × (b + c)

The problem is written as (b. × c) it must be either (b × c or b . c). Am i right?


I have tried the first one through matrices and the simple cross method the answer is (b × c)= 3j + 6k
or it is b . c thats why i am getting the wrong answer. Resolve issues.

The second is

find the value of e so that A = ci – 2j + k and B = 2ci + cj – 4k are perpendicular.

Its not e its c. I solved it by dot product as

********* A . B = ABcos90°= 0 because A B are perpendicular. But didn,t get the answer.****

Regards.
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  #13  
Old Sunday, May 24, 2015
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Quote:
Originally Posted by AZKAFATIMA View Post
Three vectors are given by:
a = 3i + 3j -2k
b = -i - 4j + 2k
c = 2i + 2j – k
Find (i) a. (b. × c), (ii) a. (b. + c), (iii) a. × (b + c)

The problem is written as (b. × c) it must be either (b × c or b . c). Am i right?


I have tried the first one through matrices and the simple cross method the answer is (b × c)= 3j + 6k
or it is b . c thats why i am getting the wrong answer. Resolve issues.

The second is

find the value of e so that A = ci – 2j + k and B = 2ci + cj – 4k are perpendicular.

Its not e its c. I solved it by dot product as

********* A . B = ABcos90°= 0 because A B are perpendicular. But didn,t get the answer.****

Regards.
It must be a.(b x c) . a.(b.c) is not possible.
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  #14  
Old Sunday, May 24, 2015
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Quote:
Originally Posted by AZKAFATIMA View Post
Three vectors are given by:
a = 3i + 3j -2k
b = -i - 4j + 2k
c = 2i + 2j – k
Find (i) a. (b. × c), (ii) a. (b. + c), (iii) a. × (b + c)

The problem is written as (b. × c) it must be either (b × c or b . c). Am i right?


I have tried the first one through matrices and the simple cross method the answer is (b × c)= 3j + 6k
or it is b . c thats why i am getting the wrong answer. Resolve issues.

The second is

find the value of e so that A = ci – 2j + k and B = 2ci + cj – 4k are perpendicular.

Its not e its c. I solved it by dot product as

********* A . B = ABcos90°= 0 because A B are perpendicular. But didn,t get the answer.****

Regards.
For second one use A.B=a1b1+a2b2+a3b3
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  #15  
Old Monday, May 25, 2015
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Quote:
Originally Posted by AZKAFATIMA View Post
Three vectors are given by:
a = 3i + 3j -2k
b = -i - 4j + 2k
c = 2i + 2j – k
Find (i) a. (b. × c), (ii) a. (b. + c), (iii) a. × (b + c)

The problem is written as (b. × c) it must be either (b × c or b . c). Am i right?


I have tried the first one through matrices and the simple cross method the answer is (b × c)= 3j + 6k
or it is b . c thats why i am getting the wrong answer. Resolve issues.

The second is

find the value of e so that A = ci – 2j + k and B = 2ci + cj – 4k are perpendicular.

Its not e its c. I solved it by dot product as

********* A . B = ABcos90°= 0 because A B are perpendicular. But didn,t get the answer.****

Regards.
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  #16  
Old Monday, May 25, 2015
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I solved it as ABcos90 and got the same answer after applying quadratic formula. There is some mistake in the problem, for we get two values not one.
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  #17  
Old Monday, May 25, 2015
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Quote:
Originally Posted by AZKAFATIMA View Post
A rod lies parallel to the x-axis of reference frame S, moving along this axis at a speed of 0.632 C. Its rest length is 1.68m. What will be its measured length in frame S?




.
Yeah it is correct. One thing which made me a bit of uncomfortable was the naming convention. Lo (L not), instead of Lp should be used. Also give the percentage at the end which tells you how much the length of a rod contracts in moving frame.

Before formula, you should also mention "Using Lorentz–FitzGerald contraction, the length observed in relative motion with the object is,".

These are just my views; you may disagree.
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  #18  
Old Monday, May 25, 2015
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If you are getting 2 answers then what is the confusion.Why you are thinking that there should be one answer. Both are correct and you can verify by putting the value of c and then taking the bot product.and your method is also correct if you are getting these 2 values.
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  #19  
Old Monday, May 25, 2015
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Agree. I'll mention it in the remaining problems. Do you possess past papers of 2003, 2004 and 2006. These are not opening on the forum.
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  #20  
Old Monday, May 25, 2015
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Quote:
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Agree. I'll mention it in the remaining problems. Do you possess past papers of 2003, 2004 and 2006. These are not opening on the forum.
No .
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