Basic Physics

Question 1

8465. If a double-acting actuating cylinder in a 3,000 psi system has a piston with a surface area of three square inches on the extension side, and a rod with a cross-section area of one square inch attached to the piston on the other side, approximately how much force will the actuator be able to produce when retracting?
      A— 9,000 pounds.
      B— 6,000 pounds.
      C— 3,000 pounds.

Answer 1

B— 6,000 pounds.

The force a hydraulic actuator can exert is determined by the area of the piston and the pressure of the fluid acting on the piston.
The effective area on the retracting side of the piston is two square inches.

2 sq. in. × 3,000 psi = 6,000 pounds of force

Question 2

8466. The boiling point of a given liquid varies
      A— directly with pressure.
      B— inversely with pressure.
      C— directly with density.

Answer 2

A— directly with pressure.

The boiling point of a liquid varies directly with the pressure above the liquid. The greater the pressure, the higher the boiling point.

Question 3

8467. Which of the following is NOT considered a method of heat transfer?
      A— Convection.
      B— Conduction.
      C— Diffusion.

Answer 3

C— Diffusion.

Heat can be transferred from a body having a high level of heat energy to a body having a lower level of heat energy by three methods: conduction (actual physical contact), convection (transfer through vertical currents), and radiation (transfer by electromagnetic waves).
Diffusion is not a method of heat transfer.

Question 4

8468. An engine that weighs 350 pounds is removed from an aircraft by means of a mobile hoist. The engine is raised 3 feet above its attachment mount, and the entire assembly is then moved forward 12 feet. A constant force of 70 pounds is required to move the loaded hoist. What is the total work input required to move the hoist?
      A— 840 foot-pounds.
      B— 1,890 foot-pounds.
      C— 1,050 foot-pounds.

Answer 4

A— 840 foot-pounds

More information is given with this problem than is needed; therefore, it can cause confusion. The only work asked for is the amount needed to move the hoist.
The hoist is moved for a distance of 12 feet and a constant force of 70 pounds is needed to move it.
The work done to move the hoist is 12 × 70 = 840 foot-pounds.

Question 5

8469. Which condition is the actual amount of water vapor in a mixture of air and water?
      A— Relative humidity.
      B— Dewpoint.
      C— Absolute humidity.

Answer 5

C— Absolute humidity.

Absolute humidity is the actual amount of water in a volume of air, and it is measured in such units as grams per cubic meter.

Question 6

8470. Under which conditions will the rate of flow of a liquid through a metering orifice (or jet) be the greatest (all other factors being equal)?
      A— Unmetered pressure, 18 psi; metered pressure, 17.5 psi; atmospheric pressure, 14.5 psi.
      B— Unmetered pressure, 23 psi; metered pressure, 12 psi; atmospheric pressure, 14.3 psi.
      C— Unmetered pressure, 17 PSI; metered pressure, 5 psi; atmospheric pressure, 14.7 psi.

Answer 6

C— Unmetered pressure, 17 PSI; metered pressure, 5 psi; atmospheric pressure, 14.7 psi.

In answering this question, we must recognize that the atmospheric pressure acts equally on both sides of the metering jet and therefore does not enter into the problem. The metering jet with the greatest pressure differential across it will have the greatest rate of flow through it.
Jet A has a pressure differential of 0.5 psi differential. Jet B has a pressure differential of 11 psi differential.
Jet C has a pressure differential of 12 psi differential.

Question 7

8471. (Refer to Figure 61.) The amount of force applied to rope A to lift the weight is
      A— 12 pounds.
      B— 15 pounds.
      C— 20 pounds.

Answer 7

B— 15 pounds.

This block and tackle supports the weight with four ropes, and this gives it a mechanical advantage of four.
To lift a 60-pound weight, a force of 15 pounds must be exerted on rope A.
Rope A will have to be pulled four times the distance the weight is lifted.

Question 8

8472. Which will weigh the least?
      A— 98 parts of dry air and 2 parts of water vapor.
      B— 35 parts of dry air and 65 parts of water vapor.
      C— 50 parts of dry air and 50 parts of water vapor.

Answer 8

B— 35 parts of dry air and 65 parts of water vapor.

Water vapor is only about 5/8 as heavy as an equal volume of dry air. The more water vapor in the air, the less the air weighs.
In choice A there is 2 percent water vapor.
In choice B there is 65 percent water vapor.
In choice C there is 50 percent water vapor.

Question 9

8473. Which is the ratio of the water vapor actually present in the atmosphere to the amount that would be present if the air were saturated at the prevailing temperature and pressure?
      A— Absolute humidity.
      B— Relative humidity.
      C— Dewpoint.

Answer 9

B— Relative humidity.

Relative humidity is the ratio of the amount of water vapor actually present in the atmosphere to the amount that would be present if the air were saturated at the prevailing temperature and pressure.

Question 10

8474. The speed of sound in the atmosphere
      A— varies according to the frequency of the sound.
      B— changes with a change in temperature.
      C— changes with a change in pressure.

Answer 10

B— changes with a change in temperature.

The speed of sound in the atmosphere varies with the temperature of the atmosphere.

Question 11

8474-1.
The speed of sound in the atmosphere is most affected by variations in which of the following?
A— Sound frequency.
B— Ambient temperature.
C— Barometric pressure.

Answer 11

B— Ambient temperature.

The speed of sound in the atmosphere varies with the ambient temperature of the atmosphere.

Question 12

8475. If the volume of a confined gas is doubled (without the addition of more gas), the pressure will (assume the temperature remains constant)
      A— increase in direct proportion to the volume increase.
      B— remain the same.
      C— be reduced to one-half its original value.

Answer 12

C— be reduced to one-half its original value.

The pressure of a gas in an enclosed container varies inversely as the volume of the container, if the absolute temperature of the gas remains constant.
Doubling the volume of the container will decrease the pressure of the enclosed gas to a value of one-half its original pressure.

Question 13

8476. If the temperature of a confined liquid is held constant and its pressure is tripled, the volume will
      A— triple.
      B— be reduced to one-third its original volume.
      C— remain the same.

Answer 13

C— remain the same.

A liquid is considered to be a noncompressible fluid. Its volume changes with a change in its temperature but it remains relatively constant as its pressure changes.
If the pressure on a confined liquid is tripled, the volume of the liquid will remain virtually the same.

Question 14

8477. How much work input is required to lower (not drop) a 120-pound weight from the top of a 3-foot table to the f loor?
      A— 120 pounds of force.
      B— 360 foot-pounds.
      C— 40 foot-pounds.

Answer 14

B— 360 foot-pounds.

Work is the product of the amount of force applied to an object times the distance through which the force causes the object to move.
As much force is needed to hold back an object when it is being lowered as it does to raise the object.
If 120 pounds of force is needed to hold back a weight as it is lowered for 3 feet, 360 foot-pounds of work has been done.

Question 15

8478. Which atmospheric conditions will cause the true landing speed of an aircraft to be the greatest?
      A— Low temperature with low humidity.
      B— High temperature with low humidity.
      C— High temperature with high humidity.

Answer 15

C— High temperature with high humidity.

The true landing speed of an aircraft is determined by the density of the air.
The amount of aerodynamic lift produced by the wing of an airplane or the rotor of a helicopter is determined by several things. Among these are the shape of the airfoil, the speed of the airfoil through the air, and the density of the air. The denser the air, the lower the speed that will produce the same amount of lift.
Density of the air depends upon both its temperature and its humidity. The hotter the air, the less dense. The more water vapor in the air (the higher its humidity), the less dense the air.
An airplane will have to fly the fastest to produce the required lift under conditions of high temperature and high humidity.

Question 16

8479. If the fluid pressure is 800 PSI in a 1/2-inch line supplying an actuating cylinder with a piston area of 10 square inches, the force exerted on the piston will be
      A— 4,000 pounds.
      B— 8,000 pounds.
      C— 800 pounds.

Answer 16

B— 8,000 pounds.

The size of the line that supplies fluid to an actuating cylinder has nothing to do with the amount of force the piston in the cylinder can exert.
When a pressure of 800 psi acts on a piston with an area of 10 square inches, a force of 800 × 10 = 8,000 pounds is produced.

Question 17

8480. In physics, which of the following factors are necessary to determine power?
      A— Force exerted, distance moved, and work.
      B— Distance moved and time required.
      C— Force exerted, distance moved, and time required.

Answer 17

C— Force exerted, distance moved, and time required.

Power is the time rate of doing work.
In order to determine the amount of work done, we must know the amount of force used and the distance through which this force acted. Force times distance is equal to work.
The amount of power needed is found by dividing the amount of work done by the time used in doing the work.
To find the amount of power needed to do a job, we must know the force, the distance, and the time.

Question 18

8481. What force must be applied to roll a 120-pound barrel up an inclined plane 9 feet long to a height of 3 feet (disregard friction)?
      L ÷ I = R ÷ E
      L = Length of ramp, measured along the slope.
      I = Height of ramp.
      R = Weight of object to be raised or lowered.
      E = Force required to raise or lower object.
      A— 40 pounds.
      B— 120 pounds.
      C— 360 pounds.

Answer 18

A— 40 pounds.

This is a simple mechanical advantage problem.
We roll the barrel three times as far as we lift it, so the force we must exert to roll the barrel up the inclined plane is only one third of the weight of the barrel.
We must exert a force of 40 pounds to roll a 120-pound barrel up the 9-foot inclined plane to lift it 3 feet.

Question 19

8482. Which statement concerning heat and/or temperature is true?
      A— There is an inverse relationship between temperature and heat.
      B— Temperature is a measure of the kinetic energy of the molecules of any substance.
      C— Temperature is a measure of the potential energy of the molecules of any substance.

Answer 19

B— Temperature is a measure of the kinetic energy of the molecules of any substance.

Heat is a form of energy, and temperature is a measure of the intensity of the kinetic energy of the molecules in a substance.
Heat energy, in the form of latent heat, can be added to an object or taken from it without changing its temperature. But, the temperature of an object changes directly with the amount of sensible heat put into it or taken from it.

Question 20

8483. What is absolute humidity?
      A— The temperature to which humid air must be cooled at constant pressure to become saturated.
      B— The actual amount of the water vapor in a mixture of air and water.
      C— The ratio of the water vapor actually present in the atmosphere to the amount that would be present if the air were saturated at the prevailing temperature and pressure.

Answer 20

B— The actual amount of the water vapor in a mixture of air and water.

Absolute humidity is the actual amount of water in a volume of air. It is measured in such units as grams per cubic meter.

Question 21

8484. The temperature to which humid air must be cooled at constant pressure to become saturated is called
      A— dewpoint.
      B— absolute humidity.
      C— relative humidity.

Answer 21

A— dewpoint.

The temperature to which a body of air must be lowered before the water vapor in the air condenses out as visible, liquid water is called the dew point of the air.

Question 22

8485. If both the volume and the absolute temperature of a confined gas are doubled, the pressure will
      A— not change.
      B— be halved.
      C— become four times as great.

Answer 22

A— not change.

The pressure exerted by a confined gas is directly proportional to its absolute temperature. If the absolute temperature is doubled, the pressure will also double.
The pressure exerted by a confined gas is inversely proportional to its volume. If its volume is doubled, the pressure will decrease to a value that is one half of the original.
If both the volume and the absolute temperature of a confined gas are doubled, the two changes will cancel each other, so the pressure of the gas will not change.

Question 23

8486. If all, or a significant part of a stall strip is missing on an airplane wing, a likely result will be
      A— asymmetrical lateral control at or near stall angles of attack.
      B— decreased lift in the area of installation at high angles of attack.
      C— asymmetrical lateral control at low angles of attack.

Answer 23

A— asymmetrical lateral control at or near stall angles of attack.

Stall strips are small triangular spoilers, or wedges, attached to the leading edge in the root area of a wing that has a tendency to stall at the tip before the root. Stalls beginning at the tip cause a loss of aileron effectiveness, and therefore lateral control, when it is most needed.
At high angles of attack, stall strips disrupt the airflow over the wing root and force it to stall before the portion of the wing ahead of the aileron.
If all or a significant part of a stall strip is missing, the stall on the affected wing will begin near the tip and decrease the effectiveness of the aileron, requiring asymmetrical lateral control at or near the stall angle of attack. More aileron deflection will be needed to raise the wing with the missing stall strip than the wing with the intact strip.

Question 24

8486-1.
The purpose of stall strips on airplane wings is to
A— increase lift in the areas of installation.
B— prevent stall in the areas of installation.
C— ensure that the wing root areas stall first.

Answer 24

C— ensure that the wing root areas stall first.

Stall strips are small triangular spoilers, or wedges, attached to the leading edge at the root area of a wing that has a tendency to stall at the tip before the root. Stalls beginning at the tip cause a loss of aileron effectiveness, and therefore lateral control, when it is most needed.
At high angles of attack, stall strips disrupt the airflow over the wing root and force it to stall before the portion of the wing ahead of the aileron.

Question 25

8487. An airplane wing is designed to produce lift resulting from
      A— positive air pressure below and above the wing’s surface along with the downward deflection of air.
      B— positive air pressure below the wing’s surface and negative air pressure above the wing’s surface along with the downward deflection of air.
      C— negative air pressure below the wing’s surface and positive air pressure above the wing’s surface along with the downward deflection of air.

Answer 25

B— positive air pressure below the wing’s surface and negative air pressure above the wing’s surface along with the downward deflection of air.

Aerodynamic lift is produced on an airfoil by the pressure difference across the airfoil along with the downward deflection of air. The pressure below the wing surface is greater than that above the wing. The pressure below the wing may be considered positive and that above the wing negative.

Question 26

8487-1.
Which of the following is Newton’s first law of motion, generally termed the law of inertia?
A— To every action there is an equal and opposite reaction. If a force is applied to an object, the object will supply a resistive force exactly equal to and in the opposite direction of the force applied.
B— Force is proportional to the product of mass and acceleration. When a force acts upon a body, the momentum of that body is changed.
C— Objects at rest tend to remain at rest and objects in motion tend to remain in motion at the same speed and in the same direction, unless acted on by an external force.

Answer 26

C— Objects at rest tend to remain at rest and objects in motion tend to remain in motion at the same speed and in the same direction, unless acted on by an external force.

Newton’s first law explains that when an object is at rest, it tries to remain at rest. But when it is moving, it tries to keep moving in a straight line and will not speed up, slow down, or turn unless it is acted upon by an outside force. This tendency of the object to remain in its original condition of motion is called inertia.

Question 27

8488. The purpose of aircraft wing dihedral is to
      A— increase lateral stability.
      B— increase longitudinal stability.
      C— increase lift coefficient of the wing. Dihedral or the wing

Answer 27

A— increase lateral stability.

upward slant of the wing from the fuselage is used to increase the lateral stability. Lateral stability is roll stability and is stability about the longitudinal axis.

Question 28

8489. Aspect ratio of a wing is defined as the ratio of the
      A— wingspan to the wing root.
      B— square of the chord to the wingspan.
      C— wingspan to the mean chord.

Answer 28

C— wingspan to the mean chord.

The aspect ratio of a wing is the ratio of the wing span to the mean, or average, chord. For a nonrectangular wing, aspect ratio is found by dividing the square of the wing span by the wing area.

Question 29

8490. A wing with a very high aspect ratio (in comparison with a low aspect ratio wing) will have
      A— increased drag at high angles of attack.
      B— a low stall speed.
      C— poor control qualities at low airspeeds.

Answer 29

B— a low stall speed.

Wings with a high aspect ratio have low drag at high angles of attack, low stalling speed, and good control at low airspeeds. Sailplanes have very high aspect ratios and fly slowly.

Question 30

8491. The desired effect of using winglets on an aircraft’s wingtips is to
      A— increase the lift to drag ratio.
      B— reduce the aspect ratio.
      C— optimize wing dihedral and improve lateral stability

Answer 30

A— increase the lift to drag ratio.

Winglets, small upturned vertical surfaces mounted on the wing tips, reduce drag by reducing the spanwise flow of air, therefore reducing vortices. The desired effect of using winglets on an aircraft’s wingtips is to increase the lift to drag (L/D) ratio of the wing.

Question 31

8491-1.
The main rotor system on a helicopter is classified in three groups. Which of those listed is NOT one of these groups?
A— The fully articulated rotor system.
B— The flexible-beam rotor system.
C— The semi-rigid rotor system.

Answer 31

B— The flexible-beam rotor system.

The classification of main rotor systems is based on how the blades move relative to the main rotor hub. The principal classifications are known as fully articulated, semi-rigid, and rigid.

Question 32

8491-2. Which of the following statements is correct?
A— When the cyclic pitch control lever is raised, the blade angle of all the rotor blades increases uniformly and they create the lift that allows the helicopter to take off vertically.
B— When the collective pitch control lever is raised, the blade angle of all the rotor blades increases uniformly and they create the lift that allows the helicopter to take off vertically.
C— When the collective pitch control lever is raised, the blade angle of the aft rotor blades decreases uniformly and they create the lift that allows the helicopter to take off vertically.

Answer 32

B— When the collective pitch control lever is raised, the blade angle of all the rotor blades increases uniformly and they create the lift that allows the helicopter to take off vertically.

The primary flight controls on a helicopter are the collective and cyclic control levers and anti-torque pedals. When the collective pitch control lever is raised, the blade angle of all the rotor blades increases uniformly and they create the lift that allows the helicopter to take off vertically. The cyclic pitch control lever, like the yoke of an airplane, can be pulled back or pushed forward (for backward or forward motion), and can be moved left and right (to bank left or right).