A bob moves in a horizontal circle tied by string. Initially it rotates at 10 rpm. If the string tension is quadrupled while keeping the radius constant, its new rotation rate is:
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A bob moves in a horizontal circle tied by string. Initially it rotates at 10 rpm. If the string tension is quadrupled while keeping the radius constant, its new rotation rate is:

G1 Physics · Accepted Answer

With fixed bob mass and radius, required string tension for circular motion is T=mω²r. Quadrupling T doubles angular speed because ω′/ω₀=√4=2. New rotation rate =2×10=20 rpm. Answer: A.