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Motion In A Plane

Question
CBSEENPH11026257

A certain vector in the xy-plane has an x-component of 4 m and a y-component of 10 m. It is then rotated in the xy-plane so that its x-component is doubled. Then, its new y-component is (approximately)

  • 20 m

  • 7.2 m

  • 5.0 m

  • 4.5 m

Solution

B.

7.2 m

Here, A= 4 i + 10 j

  A = 42 + 102

       = 16 + 100

  A = 116 m

Now, according to question,

   A = 8 i + n j

⇒ A = 82 + n2

    116 = 82 + n2

Squaring on both sides

   116 = 64 + n2

⇒ π2 = 116 - 64

     n = 7.2 m