OAR Mechanical Comprehension: Forces Questions and Answers

Question 1

Two mechanics are trying to loosen a stubborn bolt.
Mechanic A applies a 50 lb force to the end of a 1-foot wrench.
Mechanic B applies a 25 lb force to the end of a 2-foot wrench.
Assuming the forces are applied perpendicularly to the wrenches, which of the following statements is true?

Accepted Answer

They both apply the same amount of torque.

Answer

Mechanic A applies more torque.

Answer

Mechanic B applies more torque.

Answer

It is impossible to determine without knowing the angle of the force.

Question 2

A person is trying to push a heavy crate across a flat, rough floor. They find it requires a large amount of force to get the crate to start moving, but once it is moving, it takes less force to keep it sliding. Which of the following best explains this phenomenon?

Accepted Answer

The coefficient of static friction is greater than the coefficient of kinetic friction.

Answer

The coefficient of kinetic friction is greater than the coefficient of static friction.

Answer

The mass of the crate decreases once it starts moving.

Answer

The normal force increases once the crate starts moving.

Question 3

Three identical containers are filled to the same height with three different liquids: saltwater, fresh water, and oil. Saltwater is denser than fresh water, and fresh water is denser than oil. At the bottom of which container is the pressure the greatest?

Accepted Answer

The container with saltwater.

Answer

The container with oil.

Answer

The container with fresh water.

Answer

The pressure is the same in all three containers.

Question 4

A 100 lb traffic light is suspended motionless by two cables. Cable A makes a 30-degree angle with the horizontal ceiling, and Cable B makes a 60-degree angle with the horizontal ceiling. Which cable experiences greater tension?

Accepted Answer

Cable A (the one with the smaller angle to horizontal).

Answer

Both cables experience the same tension.

Answer

It is impossible to determine without knowing the cable lengths.

Answer

Cable B (the one with the larger angle to horizontal).

Question 5

Which of the following modifications to a large cargo truck would most effectively increase its stability and make it less likely to tip over on a sharp turn?

Accepted Answer

Loading the heaviest items on the bottom of the cargo area.

Answer

Increasing the height of the cargo load.

Answer

Using narrower tires.

Answer

Inflating the tires to a higher pressure.

Question 6

A jet engine provides thrust to propel an airplane forward. According to Newton's Third Law of Motion, what is the 'reaction' force that pushes the airplane forward?

Accepted Answer

The force of the hot exhaust gases being pushed backward out of the engine.

Answer

The force of the air outside the plane pushing back against the front of the engine.

Answer

The force of the engine's internal parts pushing on the air inside the combustion chamber.

Answer

The force of the wings creating lift.