Free OAR Mechanical Reasoning Question and Answers

Question 1

What temperature will ice be formed from mineral water?

Accepted Answer

Less than 0 degrees celsius

Answer

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?

Accepted Answer

Exiting the muzzle

Answer

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?

Accepted Answer

Pulley A

Answer

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?

Accepted Answer

30 times

Answer

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?

Accepted Answer

closer to the large mass

Answer

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.

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Free OAR Mechanical Reasoning Question and Answers