Free OAR Mechanical Reasoning Question and Answers — Questions and Answers

Question 1: What temperature will ice be formed from mineral water?

Less than 0 degrees celsius (Correct answer)
0 degrees celsius
Cannot say
More than 0 degrees celsius

Correct answer: Less than 0 degrees celsius

Pure water freezes at 0 degrees Celsius. However, mineral water contains dissolved salts and other impurities. These dissolved substances cause a phenomenon known as freezing point depression, which means the water will freeze at a temperature slightly lower than 0 degrees Celsius.

Question 2: A ship is launched up toward a mountain range by a cannon. Where will the projectile's maximum velocity be, disregarding air resistance?

As it impacts the mountains
Exiting the muzzle (Correct answer)
Halfway to the mountains
None of the above

Correct answer: Exiting the muzzle

Disregarding air resistance, a projectile's maximum velocity occurs at the moment it receives its initial propulsion. For a cannon-launched projectile, this is when it exits the muzzle, as it has the full force of the explosion propelling it. After this point, gravity begins to act on it, continuously reducing its vertical velocity component, and thus its overall speed will decrease until impact.

Question 3: These pulleys are connected by belts. Which pulley moves the most quickly?

Pulley C
Pulley A (Correct answer)
Pulley B

Correct answer: Pulley A

When pulleys are connected by belts, the linear speed of the belt is constant across all pulleys. To maintain this constant belt speed, a smaller pulley must rotate at a higher angular velocity (revolutions per minute) than a larger pulley. Since Pulley A is the smallest in diameter, it will move the most quickly in terms of rotations per minute.

Question 4: How many times does Gear C rotate in 3 minutes if Gear A is moving at 10 rotations per minute?

3 times
30 times (Correct answer)
1.7 times

Correct answer: 30 times

To determine the rotations of Gear C, we need to know the gear ratios between A, B, and C. Assuming a common gear setup where the final gear (C) rotates at the same speed as the initial gear (A) due to specific gear sizes (e.g., A and C are the same size, and B is an idler gear or the ratios cancel out), if Gear A rotates at 10 rotations per minute (RPM), then Gear C also rotates at 10 RPM. Over 3 minutes, Gear C would complete 10 rotations/minute * 3 minutes = 30 rotations.

Question 5: To balance this beam, where should the fulcrum be placed?

closer to the small mass
exactly between the two masses
closer to the large mass (Correct answer)

Correct answer: closer to the large mass

To balance a beam, the principle of moments states that the clockwise moment must equal the anticlockwise moment. This means the product of mass and distance from the fulcrum must be equal on both sides. If one mass is significantly larger, the fulcrum must be placed closer to that larger mass to reduce its lever arm and create an equal balancing force with the smaller mass, which will have a longer lever arm.

Question 6: Which direction will demand more pulling power?

both orientation are equal
with the rope at an angle to the table (Correct answer)
with the rope parallel to the table

Correct answer: with the rope at an angle to the table

When pulling an object with the rope at an angle to the table, only the horizontal component of your pulling force contributes to moving the object forward. The vertical component of the force is directed upwards, reducing the effective horizontal force. To achieve the same effective horizontal pulling force as pulling parallel to the table, you must apply a greater total force along the angled rope, thus demanding more pulling power from the person.

Question 7: The horizontal surface area of the larger piston is four times that of the smaller piston. How much farther will the larger piston go if the smaller piston is compressed by 8 inches?

2 inches (Correct answer)
32 inches
8 inches

Correct answer: 2 inches

In a hydraulic system, the volume of fluid displaced by the smaller piston must equal the volume displaced by the larger piston. Since volume is calculated as area multiplied by distance, if the larger piston has four times the surface area of the smaller piston, it will move only one-fourth the distance for the same volume of fluid displacement. Therefore, if the smaller piston is compressed by 8 inches, the larger piston will move 8 inches / 4 = 2 inches.

Free OAR Mechanical Reasoning Question and Answers

What temperature will ice be formed from mineral water?