The GATE Grind

GATE 2026 ME – Question 17

Theory of Machines · Gears and gear trains · 1 mark · Multiple choice

A gear train with five gears is shown in the figure below. The number of teeth on each gear is $N_1$, $N_2$, $N_3$, $N_4$, and $N_5$. The idler gear in this gear train is

Five gears in a row. Gear 1 (the driver) meshes with gear 2. Gears 2 and 3 are on the same shaft. Gear 3 meshes with gear 4, and gear 4 meshes with gear 5 (the driven gear).
  1. gear 4
  2. gear 2
  3. gear 3
  4. gear 1

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Show answer and explanation

Correct answer: (A) gear 4

Explanation

An idler gear meshes with a gear before it and a gear after it and does not change the speed ratio of the train. Gear 4 meshes with gear 3 and gear 5, so it is the idler. Gears 2 and 3 are fixed on one shaft (a compound gear) and do change the ratio.