Disc 1 has mass 2 kg, radius 0.2 m and angular speed 50 rad/s. Disc 2 has mass 4 kg, radius 0.1 m and angular speed 200 rad/s in the same sense. They touch coaxially and eventually co-rotate. Find final angular speed.
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Question

Disc 1 has mass 2 kg, radius 0.2 m and angular speed 50 rad/s. Disc 2 has mass 4 kg, radius 0.1 m and angular speed 200 rad/s in the same sense. They touch coaxially and eventually co-rotate. Find final angular speed.

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G1 Physics · Accepted Answer

Step 1: I₁=½×2×0.2²=0.04 kg·m²; I₂=½×4×0.1²=0.02 kg·m². Step 2: With no external torque, ωf=(I₁ω₁+I₂ω₂)/(I₁+I₂)=(0.04×50+0.02×200)/0.06=100 rad/s. Final answer: B — 100 rad/s.