Reflecting mirror

Classical Mechanics Level 4

A ray of light travelling in the direction 1 2 ( i ^ + 3 j ^ ) \frac12 \Big( \hat i + \sqrt 3 \hat j \Big) is incident on a plane mirror.
After reflection, it travels along the direction 1 2 ( i ^ − 3 j ^ ) \frac12 \Big( \hat i - \sqrt 3 \hat j \Big) .

Find the angle of incidence.

6 0 ∘ 60^\circ 4 5 ∘ 45^\circ 3 0 ∘ 30^\circ 7 5 ∘ 75^\circ

A Former Brilliant Member by A Former Brilliant Member

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1 solution

i know it's too easy but i got a doubt....here is what i did.. took dot of both vectors given this should give me twice the required angle but their dot gives -1

so 2*angle=pi

ans pi/2 ............what's wrong in it ??

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Nahh dot will be -1/2

Prakhar Bindal - 4 years, 1 month ago

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(1-3)/2==-1 ....nahi bhai ?

A Former Brilliant Member - 4 years, 1 month ago

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Do do half h dhang se padh

Prakhar Bindal - 4 years, 1 month ago

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@Prakhar Bindal – bhai matlab ? 1-3/2 hi toh h ?

A Former Brilliant Member - 4 years, 1 month ago

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@A Former Brilliant Member – Bhai dono vectors ke bahar half h .

Prakhar Bindal - 4 years, 1 month ago

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@Prakhar Bindal – achaaa.... do br half krna tha kya bhai asi hi to glti hoti muhjse ......sorry.

A Former Brilliant Member - 4 years, 1 month ago

ok even if dot is -0.5.....the ans would come 60 as cos(120)=(-0.5) :P this ans is again wrong.

A Former Brilliant Member - 4 years, 1 month ago

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