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All questions of Vectors for SSS 2 Exam

If 14511_image012 what is the angle between 14511_image013 and 14511_image014
  • a)
    900
  • b)
    300
  • c)
    600
  • d)
    450
Correct answer is option 'D'. Can you explain this answer?

Gaurav Kumar answered
We know that for two vectors P and Q
P.Q = |P||Q| cos a
And PxQ = |P||Q| sin a
Where a is angle between them
When P.Q = PxQ
We get sin a = cos a
Thus a = 450

In the triangle ABC, which statement is not true?
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'D'. Can you explain this answer?

sanju sura answered
Ab + bc > ac ...it is property of a triangle .... that sum of two sides is greater than the third side ... so I think it is no possible that ab +bc -ca =0...but I'm not understanding the logic behind the question.......😊

The points with position vectors  are collinear vectors, Value of a =​
  • a)
    -20
  • b)
    20
  • c)
    -40
  • d)
    40
Correct answer is option 'C'. Can you explain this answer?

Om Desai answered
Position vector A = 60i+3j
Position vector B = 40i-8j
Position vector C = aj-52j
Now, find vector AB and BC
AB = -20i-11j
BC= (a-40)i-44j
To be collinear,  angle between the vector AB and BC made by the given position vectors should be 0 or 180 degree.
That’s why the cross product of  the vectors should be zero
ABXBC=(-20i-11j)X(a-40)i-44j
0i+0j+(880+11(a-40))=0
a-40= -80
a=-40
Therefore, a should be -40 to be the given positions vectors collinear.

The vector joining the points A(2, – 3, 1) and B(1, – 2, – 5) directed from B to A is:
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'D'. Can you explain this answer?

Siddhant Kumar answered
The vector goes from B to A means that its initial coordinates is at B and final at A.
so the vector BA will be [ (2-1)i + (-3+2) j + (1+5)k ] = i-j+6k.

Direction of the resultant of two vectors is given by
  • a)
    cos-1(Ay + By/Ax + Bx)
  • b)
    cos-1(Ax + By/Ay + Bx)
  • c)
    tan-1(Ay + By/Ax + Bx)
  • d)
    tan-1(Ay - By/Ax - Bx)
Correct answer is option 'C'. Can you explain this answer?

Lakshmi Sharma answered
Assume the two vector A and B with an angle alpha whose resultant be vector C given by vector C = vector A + vector B. In addition drop a line from the point B and C meeting to form the right angled triangle, so AC2 = AD2 + CD2
⇒  
⇒ 
⇒ 
⇒ From triangle BCD, cos alpha = BD / BC
⇒ BD = BC x cos∝
⇒ 
⇒ 
The resultant vector makes angle theta therefore, in triangle BCD,
sin∝ = CD/BC
⇒ CD = BCsinα,
and  in triangle ADC,
tanθ = CD/AD = BC sinα/a + bcos∝
⇒ θ = tan -1 bsin∝/a + bcosα

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