Question 53 3AE02 - Third Assistant Engineer (Alt)

The Correct Answer is A ### Explanation of Correct Option (A) Option A is correct because it accurately describes the fundamental operation and characteristics of a single reduction gear set, which is designed to reduce speed (and increase torque) from the input shaft to the output shaft. 1. **Pinion vs. Gear Size:** The gear that provides the input power is called the **pinion** (or drive gear). In almost all standard reduction gearboxes, the pinion is intentionally made **smaller** than the mating gear (the driven gear). This size difference (number of teeth) is what creates the speed reduction ratio. 2. **Speed Relationship (Reduction):** Since the setup is a "reduction" gear: * The input shaft (connected to the pinion) must rotate **faster** than the output shaft. Therefore, the drive pinion rotates at a relatively **high speed**. * The output shaft (connected to the larger driven gear) must rotate **slower** than the input shaft. Therefore, the driven gear rotates at a relatively **low speed**. Thus, the statement "The drive pinion is the smaller of the two gears and rotates at a relatively high-speed. The driven gear is the larger of the two gears and rotates at a relatively low speed" is the definition of a standard speed reduction gearing setup. --- ### Explanation of Incorrect Options **B) The drive pinion is the smaller of the two gears and rotates at a relatively low speed. The driven gear is the larger of the two gears and rotates at a relatively high-speed.** * **Incorrect Speeds:** This option contradicts the definition of a reduction gear. If the smaller pinion rotated at a low speed and the larger driven gear rotated at a high speed, the system would be increasing speed (an overdrive system), not performing a speed reduction. **C) The drive pinion is the larger of the two gears and rotates at a relatively high speed. The driven gear is the smaller of the two gears and rotates at a relatively low speed.** * **Incorrect Size and Speed Relationship:** This configuration (large pinion driving small gear) describes an overdrive (speed increasing) setup, where the driven gear would rotate at a high speed. Furthermore, standard practice for reduction gears is to use a smaller pinion for the input and a larger gear for the output. **D) The drive pinion is the larger of the two gears and rotates at a relatively low speed. The driven gear is the smaller of the two gears and rotates at a relatively high-speed.** * **Incorrect Size and Speed Relationship:** Like option C, this describes an overdrive system (large gear driving small gear), which increases the speed. Since the question specifies a *reduction* gear, this scenario is incorrect. The smaller gear should be the driven gear and rotate at a high speed only if the system were designed for speed increase, which contradicts the problem's premise.