A concave mirror of focal length 20 cm moves right at 2 cm/s. An object 30 cm to its left moves right at 5 cm/s. What is the image velocity relative to the mirror in magnitude?
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A concave mirror of focal length 20 cm moves right at 2 cm/s. An object 30 cm to its left moves right at 5 cm/s. What is the image velocity relative to the mirror in magnitude?

G1 Physics · Accepted Answer

Object velocity relative to mirror is 5−2=3 cm/s. At u=30 cm, |m|=2, so axial image speed relative to mirror has magnitude 4×3=12 cm/s.