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Motion In Straight Line

Question
CBSEENPH11020518

If the magnitude of sum of two vectors is equal to the magnitude of difference of the two vectors, the angle between these vectors is,

  • 90o

  • 45o

  • 180o

  • 0o

Solution

A.

90o

There are two vectors P and Q.
It is given that,
open vertical bar straight P plus straight Q close vertical bar space equals open vertical bar P minus Q close vertical bar
Let, angle between P and Q is straight ϕ,
straight P squared plus straight Q squared space plus space 2 PQ space cosϕ space equals space straight P squared space plus space straight Q squared space minus space 2 space PQ space cos space straight ϕ
rightwards double arrow space 4 PQ space cos space straight ϕ space equals space 0

rightwards double arrow space cos space straight ϕ space equals space 0 space left square bracket because space straight P comma space straight Q space not equal to space 0 right square bracket

rightwards double arrow space straight ϕ space equals space straight pi over 2 equals space 90 to the power of straight o