
∣B∣=∣A∣
∣B−A∣=∣A∣2+∣A∣2+2∣A∣∣A∣cos(180∘−Δθ)
=∣A∣2+∣A∣2−2∣A∣2cosΔθ
=2∣A∣2−2∣A∣2cosΔθ
=2∣A∣2(1−cosΔθ)
∵1−cosΔθ=2sin2(2Δθ)
=2∣A∣2×2sin2(2Δθ)
=2∣A∣sin(2Δθ)
For small Δθ,sin(2Δθ)≃(2Δθ)
∣B−A∣=2∣A∣(2Δθ)
=∣A∣Δθ
JEE Main 2015 — Physics Mechanics
A vector A is rotated by a small angle Δθ radians (Δθ≪1) to get a new vector B . In that case ∣B−A∣ is :
Held on 11 Apr 2015 · Verified 6 Jul 2026.
∣A∣[1−2(Δθ)2]
0
∣A∣Δθ
∣B∣Δθ−∣A∣
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