A point object is 30 cm in front of a convex mirror of focal length 15 cm and approaches the mirror at 8 cm/s along the axis. What is the magnitude of image speed?
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A point object is 30 cm in front of a convex mirror of focal length 15 cm and approaches the mirror at 8 cm/s along the axis. What is the magnitude of image speed?

G1 Physics · Accepted Answer

For a convex mirror, |v|=fu/(u+f)=15×30/45=10 cm, so |v/u|=1/3. Axial speed amplification=(1/3)²=1/9, giving 8/9 cm/s.