A point object is moving with velocity 6î + 2ĵ + k̂ m s⁻¹ in front of a plane mirror whose reflecting side is the x-z plane. If the mirror also moves with velocity î - ĵ m s⁻¹, what is the speed of the image in m s⁻¹, rounded off to the nearest integer?
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Question

A point object is moving with velocity 6î + 2ĵ + k̂ m s⁻¹ in front of a plane mirror whose reflecting side is the x-z plane. If the mirror also moves with velocity î - ĵ m s⁻¹, what is the speed of the image in m s⁻¹, rounded off to the nearest integer?

Options

G1 Physics · Accepted Answer

Derived solution: Step 1: Use the law of reflection i = r and plane-mirror symmetry. The image is as far behind the mirror as the object is in front; rotation of a mirror by φ rotates the reflected ray by 2φ. Step 2: Substitute the values given in the question and apply the geometry/sign convention shown. Step 3: On simplification the result is 7. Therefore the correct option is B.