GCAT - General Cognitive Ability Mechanical Reasoning Concepts Questions and Answers — Questions and Answers
Question 1: In the gear system shown, the driver gear 'A' rotates clockwise. Gear 'A' meshes with gear 'B'. Gear 'B' and gear 'C' are fixed on the same axle. Gear 'C' meshes with gear 'D'. In which direction will gear 'D' rotate?
- It will not rotate.
- Counter-clockwise.
- Clockwise. (Correct answer)
- The direction depends on the gear sizes.
Correct answer: Clockwise.
When two gears mesh, they rotate in opposite directions. Since gear 'A' rotates clockwise (CW), gear 'B' will rotate counter-clockwise (CCW). Because gears 'B' and 'C' are on the same axle, gear 'C' also rotates counter-clockwise (CCW). Since gear 'C' (CCW) meshes with gear 'D', gear 'D' will rotate in the opposite direction, which is clockwise (CW).
Question 2: A lever is balanced on a fulcrum. A weight of 20 kg is placed 3 meters to the left of the fulcrum. To maintain the balance, where must a weight of 15 kg be placed?
- 4 meters to the right of the fulcrum. (Correct answer)
- 3 meters to the right of the fulcrum.
- 5 meters to the left of the fulcrum.
- 2.25 meters to the right of the fulcrum.
Correct answer: 4 meters to the right of the fulcrum.
The principle of moments states that for a lever to be in balance, the clockwise moment must equal the counter-clockwise moment. The moment is calculated as Force (or weight) × Distance from the fulcrum. The moment on the left is 20 kg × 3 m = 60 kg·m. To balance this, the moment on the right must also be 60 kg·m. Therefore, 15 kg × Distance = 60 kg·m. Solving for the distance gives 60 / 15 = 4 meters.
Question 3: Which of the following pulley systems requires the least amount of effort (force) to lift the same load, assuming the pulleys and ropes are weightless and frictionless?
- A single fixed pulley.
- A system with two fixed pulleys.
- A system with one fixed and one movable pulley.
- A system with one fixed and two movable pulleys. (Correct answer)
Correct answer: A system with one fixed and two movable pulleys.
The effort required to lift a load is determined by the mechanical advantage (MA) of the pulley system. Movable pulleys increase the mechanical advantage. A single fixed pulley has an MA of 1. Two fixed pulleys also have an MA of 1. A system with one fixed and one movable pulley has an MA of 2. A system with one fixed and two movable pulleys has an MA of 4. The system with the highest mechanical advantage requires the least effort.
Question 4: A sealed hydraulic system operates based on Pascal's principle. If the input piston has a surface area of 5 cm² and the output piston has a surface area of 25 cm², what is the resulting output force if a force of 100 Newtons is applied to the input piston?
- 20 Newtons
- 500 Newtons (Correct answer)
- 100 Newtons
- 2500 Newtons
Correct answer: 500 Newtons
According to Pascal's principle, pressure is transmitted equally throughout an enclosed fluid (P1 = P2). Since Pressure = Force / Area, we have F1/A1 = F2/A2. Plugging in the values: 100 N / 5 cm² = F2 / 25 cm². This simplifies to 20 N/cm² = F2 / 25 cm². To find F2, multiply the pressure by the output area: F2 = 20 N/cm² * 25 cm² = 500 Newtons.
Question 5: Two people need to load an identical, heavy box onto a truck bed of the same height. Person A lifts the box straight up. Person B pushes the box up a long, frictionless ramp. Which statement accurately compares the work done and the force required?
- Person B uses less force and does less work.
- Both persons do the same amount of work, but Person A uses more force. (Correct answer)
- Person A does less work because the distance is shorter.
- Person B uses more force because the distance is longer.
Correct answer: Both persons do the same amount of work, but Person A uses more force.
Work is defined as Force × Distance. While Person A (lifting) travels a shorter distance, they must apply a large force equal to the box's weight. Person B (using a ramp) applies a smaller force over a longer distance. Because the final height (and thus the change in potential energy) is the same, the total amount of work done is the same for both people, assuming no friction. The ramp provides a mechanical advantage, reducing the required force.
Question 6: Water is flowing from a wide pipe into a narrower pipe. Assuming the flow is continuous and the pipe is horizontal, what happens to the speed and pressure of the water as it enters the narrower section?
- The speed decreases and the pressure increases.
- The speed increases and the pressure increases.
- The speed decreases and the pressure decreases.
- The speed increases and the pressure decreases. (Correct answer)
Correct answer: The speed increases and the pressure decreases.
This scenario is explained by the principles of continuity and Bernoulli's principle. The continuity equation states that for an incompressible fluid, the product of cross-sectional area and velocity must be constant. Therefore, as the pipe's area decreases, the water's speed must increase. Bernoulli's principle states that for a fluid in motion, an increase in speed occurs simultaneously with a decrease in pressure. Thus, in the narrower section, the speed is higher and the pressure is lower.
GCAT - General Cognitive Ability Mechanical Reasoning Concepts Questions and Answers
In the gear system shown, the driver gear 'A' rotates clockwise.
Gear 'A' meshes with gear 'B'.
Gear 'B' and gear 'C' are fixed on the same axle.
Gear 'C' meshes with gear 'D'.
In which direction will gear 'D' rotate?