The RPM of "A" is 100 and hobbed with 80...

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Question 1 of 205eccefa3bacbc34ba4d47ce3

The RPM of "A" is 100 and hobbed with 80 teeth. If gears "B", "C", and "D" have 62, 20, and 38 teeth respectively, the RPM of "D" in the gear train illustration is __________. See illustration MO-0088.

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🔍 Key Concepts

• Use the basic gear relationship N₁ × T₁ = N₂ × T₂ (speed × teeth) for each meshing pair • In a compound gear train, gears fixed on the same shaft (like B and C) have the same RPM • The overall speed ratio from A to D is the product of the individual gear ratios across the train

💭 Think About

• First, use A’s speed (100 RPM) and its teeth (80) with gear B’s teeth (62) to find the RPM of B • Since B and C are on the same shaft, use B’s RPM as C’s RPM, then use C’s teeth (20) and D’s teeth (38) to find D’s RPM • Compare the final RPM you calculate for D with the choices and think about whether the result should be faster or slower than 100 RPM based on the tooth counts

✅ Before You Answer

• Verify which gears actually mesh in the illustration: A meshes with B, and C meshes with D • Confirm that you used the inverse relationship correctly: fewer teeth → higher RPM, more teeth → lower RPM • Recheck that you multiplied the two stage ratios, rather than adding them, when going from A to D

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