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Question
Physics
A vector vecA is rotated by a small angle Δθ radians (Δθ<<1) to get a new vector vecB. In that case | vecB- vecA| is ;
Q. A vector
A
is rotated by a small angle
Δ
θ
radians
(
Δ
θ
<<
1
)
to get a new vector
B
.
In that case
∣
∣
B
−
A
∣
∣
is ;
5157
243
JEE Main
JEE Main 2015
Motion in a Plane
Report Error
A
0
19%
B
∣
∣
A
∣
∣
(
1
−
2
Δ
θ
2
)
19%
C
∣
∣
A
∣
∣
Δ
θ
37%
D
∣
∣
B
∣
∣
Δ
θ
−
∣
∣
A
∣
∣
26%
Solution:
∣
B
−
A
∣
=
A
2
+
B
2
+
2
A
B
cos
(
π
−
Δ
θ
)
⇒
since
∣
A
∣
=
∣
B
∣
=
A
,
cos
(
π
−
Δ
θ
)
=
−
cos
Δ
θ
=
2
A
2
(
1
+
cos
(
π
−
Δ
θ
)]
=
2
A
2
2
cos
2
(
2
π
−
Δ
θ
)
=
2
A
cos
(
2
π
−
2
Δ
θ
)
=
2
A
sin
(
2
Δ
θ
)
sin
Δ
θ
<
sin
(
2
Δ
θ
)
≈
2
Δ
θ
⇒
∣
B
−
A
∣
=
A
Δ
θ