Question:

The value of P so that the vectors $2 \hat i - \hat j + \hat k, \hat i + 2 \hat j - 3 \hat k$ and $3 \hat i + P \hat j + 5 \hat k$ are coplanar should be

Updated On: Jul 7, 2022
  • 16
  • -4
  • 4
  • -8
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The Correct Option is B

Solution and Explanation

For coplanarity $35mm \begin{vmatrix} 2 & -1 & 1\\ 1 & 2 & -3\\ 3 & P & 5\\ \end{vmatrix} = 0$ or $ 2(10 + 3P) + 1(5 + 9) +1(P - 6)=0$ or $ 20 + 6P + 5 + 9 + P - 6 = 0$ or $ 7P + 34 - 6 = 0$ or $ 7P + 28 = 0$ or $ 7P = -28$ $\Rightarrow P = - \frac{28}{7} = -4$
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Concepts Used:

Motion in a Plane

It is a vector quantity. A vector quantity is a quantity having both magnitude and direction. Speed is a scalar quantity and it is a quantity having a magnitude only. Motion in a plane is also known as motion in two dimensions. 

Equations of Plane Motion

The equations of motion in a straight line are:

v=u+at

s=ut+½ at2

v2-u2=2as

Where,

  • v = final velocity of the particle
  • u = initial velocity of the particle
  • s = displacement of the particle
  • a = acceleration of the particle
  • t = the time interval in which the particle is in consideration