# ASVAB Mechanical Comprehension Test

#### How much force is needed to lift the 10Kg weight?

In a double-pulley system, the force is equal to the weight divided by two. It will require a 5 Kg force to lift a 10Kg weight.

#### The smaller gear has 8 teeth, and the larger gear has 16 teeth. When the larger gear makes 12 revolutions, how many revolutions will the smaller gear make?

#### Which of the following is the basis for Pascal’s Law?

The third principle of hydraulics is the basis for Pascal’s Law and states that when pressure is applied to a fluid, the pressure is transmitted evenly throughout – in other words, how force is amplified within a hydraulic system.

#### An 80-lb child is sitting on one end of a seesaw. If another 80-lb child jumps from a high platform onto the other end of the seesaw, what will happen?

The force of the second child landing on the seesaw will propel the other end of the seesaw into the air.

#### What is a vector quantity?

Gravity is a type of force, and since force has magnitude and direction it is known as a vector quantity.

#### Which of the following describes the relationship between kinetic energy, mass, and velocity?

An object’s kinetic energy is defined as KE = ½(mv^{2}
). Reorienting, we find: 2KE = mv^{2}
.

#### One horsepower is equivalent to

Horsepower is a unit used to rate internal combustion engines. One horsepower is the equivalent of 746 watts.

#### What type of simple machine is pictured above?

This machine pictured is a second-class lever. An example of a second-class lever is a wheelbarrow.

#### At minimum, how many pulleys are there in a block and tackle system?

The block and tackle pulley system requires at least two or more pulleys. The bare minimum for this system is two.

#### When torque increases, speed

The quantities of torque and speed are inversely proportional. When one increases, the other decreases.

#### If a wedge is made longer relative to its height, how does the force increase?

When the distance of a life is the same as the distance the initial force travels, the force in will equal the force out. Making the wedge longer relative to its height (less slope) will change this by decreasing the amount of lift that takes place as the wedge is moved horizontally.

#### If a man uses 200 N of force over a distance of 50 meters, how many joules of work are performed?

Work is defined as the product of force in the direction of displacement. Here a force of 200 N is used over a displacement of 50 m. Consequently, the work performed is 200 N * 50 m = 10,000 J.

#### What is a component of potential energy?

An object’s potential energy is equal to its mass times its acceleration due to gravity times its height, or PE = mgh.

#### A fish tank at an aquarium contains several cubic feet of water (1 cubic foot of water = 62.5 pounds). If the fish tank is 6 feet deep, 12 feet wide, and 13 feet long, what’s the approximate pressure at the bottom of the tank in pounds per square inch?

To find the pressure (psi), we must divide the tank’s total volume by the surface area of the bottom of the tank. The volume = 6 x 12 x 13 = 936 feet. Multiply it by 62.5 to convert it into pounds: 936 x 62.5 = 58,500. The bottom of the tank’s surface area is 12 ft x 13 ft = 144 inches x 156 inches. Since pressure is in pounds per square inch (psi), we have to convert to inches. The surface area is 22,464 inches. The psi is 58,500 / 22,464 is approximately 2.6.

#### If Gear A turns counterclockwise, what other gears turn counterclockwise?

#### The well pictured above uses what type of simple machine to raise and lower a bucket?

The well pictured here uses a wheel and axle system. The movement at the wheel becomes smaller than the movement on the shaft, increasing the force on the shaft.

#### Weight is the

Mass is the amount of matter in an object; weight is the force exerted on an object due to gravity.

#### What is the advantage of a single pulley?

A single pulley changes the direction of effort: you pull the rope down in order to lift the object up instead of pushing up. The same amount of effort is required as without a pulley.

#### A farmer is attempting to pull a log with a line of rope attached to a tractor. Where should she watch for breakage on the rope?

The tension on the rope nearest to the tractor is the greatest. This is because tension is greatest where the force is being applied.

#### If a large gear drives a smaller gear, which of the following will not occur?

The ratio of the gears (a comparison of the number of teeth on the gears) will remain the same.

#### "For every action there is an equal and opposite reaction" best summarizes which of Newton's Laws of Motion?

Newton's third law explains that for every action there is an equal and opposite reaction.

#### How is a wedge different from an inclined plane?

A wedge, unlike a slide, is useful in motion. For example, a knife slicing through a carrot.

#### Jeremy chucks a baseball as far as he can. His arm is operating as a

A third class lever magnifies force in the same direction that it is applied, and the force is applied at a point between the fulcrum and the object.

#### The measure of the quantity of matter in an object is its

Mass is the amount of matter in an object. Usually, but not always, an object with a larger volume has a larger density (like an elephant, for instance, versus a mouse).

#### Simple machines are useful in that they

Simple machines amplify the effort put into a task. For instance, a pulley allows a person to lift a much heavier load than they otherwise would be capable of.

#### In terms of force, what makes hydraulic jacks so useful?

Hydraulic jacks are useful because the liquids used to transmit force do not compress, even under high pressure. Instead, that force is transmitted to another location.

#### Energy is

Energy is the capacity to do work: to change something.

#### Work occurs when

Work occurs when force is used to move something, overcoming resistance, over a certain distance. Work results in movement, otherwise, it is just force. Work is calculated by multiplying force by distance. The formula is W=Fd. Work is measured in joules, force is measured in newtons, and distance is measured in meters.

#### Which of the following is the best example of an inclined plane?

A slide is the best example of an inclined plane,. It is a surface tilted at an angle used for raising or lowering objects.

#### Power is the

Power is the rate at which work is performed—the rate at which force is successfully applied over a distance.

#### What is the mechanical advantage of a teeter-totter built so that each seat is 2 meters from the fulcrum?

The mechanical advantage is the ratio of the distance between the fulcrum and the point at which force is applied, and the distance between the fulcrum and the object being acted upon.

#### 15 J of work were expended moving an 18 kg block. At what velocity did the block move?

To solve for velocity, you should use the formula W = KE, where Work = W, and Kinetic Energy = KE. This is because any work that is done to accelerate an object is converted to the kinetic energy of that object (the work-energy theorem). So, W = (1/2) mv2. Plugging in the block's weight (18 kg) and the work done (15 J) will give you a velocity of 1.3 m/s.

#### What is the potential energy of a 4 lb. book held 50 feet in the air?

Potential energy is calculated by multiplying mass (in kilograms), acceleration due to gravity, and height (in meters). Thus, the potential energy of the book is 268.128 J: 1.8 kilograms multiplied by 15.2 meters multiplied by 9.8 m/s2.

#### A 180 pound person dives off of a 30 foot cliff. What is their velocity as they enter the water?

In this situation, potential energy equals the final kinetic energy: PE = KE. After converting feet to meters, solving for v (velocity) give us an answer of 13 m/s.

#### A perfectly efficient machine

A machine that is 100% efficient converts all of the power applied to it into output force. This is highly unlikely due to wear and tear, friction, and general imperfections.

#### You're trying to replace a flat. How much torque are you applying to a wheel nut if you're applying 40 pounds with a wrench measuring 9"?

Torque is calculated by multiplying force (in pounds) and length (in feet). Thus, 40 pounds multiplied by .75 feet gives us 30 ft-lb of torque.

#### What is the point at which the lever pivots?

The fulcrum of a lever is the support point on which the lever pivots, like the centerpoint of a see-saw. A lever is a simple machine, meaning that it amplifies an input force to provide a greater output force. The fulcrum's position affects the type of lever and the mechanical advantage provided by it.

#### Tension can best be called

Tension is the internal stretch force of an object like a rope.

#### Which of the following situations requires overcoming the least amount of kinetic friction?

Objects with more weight have more frictional force; thus, moving that heavier objects requires greater force. Additionally, the icy path has a lower coefficient of friction than the regular path. Because of these factors, the empty box on the icy path will be the easiest to move.

#### Which of the following is not a unit of power?

A newton is a unit of force, not power. Force is push (like a person pushing on box) or a pull (like the pull of Earth's gravity).

#### A lever

A lever both compounds force (makes it easier for you to lift something) and changes direction (when you push down on a lever, the object is lifted).

#### The wheel of a car has a diameter of 16 inches and moves a smaller wheel of 4 inches. What is the mechanical advantage gained by the system?

This systems achieves a mechanical advantage of 4:!. This is a reflection of the difference in the diameters of the wheels. The two diameters (16 inches and 4 inches) have a ratio of 16:4, which is equal to 4:1.

#### When a machine compounds the force you use, it gives you a(n)

Mechanical advantage is the advantage gained by using a simple machine to complete a task. It is a measure of the force amplification that occurs when we use tools like levers or gears or pulley systems.

#### Which of the following wedges generates the greatest amount of force.

When a wedge is longer in relation to its height it decreases the amount of lift that occurs when the wedge moves through an object. This increases the amount of force generated.

#### Which of the following is an example of potential energy?

Potential energy is energy that can be converted to movement, like a diver about to jump. Potential energy is dependent on an object's position. For example, a diver at the top of a tall cliff has considerable potential energy. Potential energy is measured in joules (J).

#### Gears are used to

Multiple gears in succession can be used to change rotation speed, as well as torque. Certain gear arrangements can result in mechanical advantage, meaning that they are considered simple machines. This is dependent on the gear ratio.

#### How many kilograms is a cow on a trailer if 1200 newtons of force are acting on it?

Weight, or newtons of force due to gravity, is calculated using the formula: W=mg. Here, W is the weight in newtons (N), m is mass (in kilograms) and g is acceleration due to gravity (which, on Earth, is always 9.8 m/s2). Solving for mass, then, requires that you divide weight (1,200 N) by gravity (9.8 m/s2). This gives you a mass of about 122 kg.

#### What measures how much force is applied to an object in order to rotate it?

Torque is how much force is acting on a object, causing it to rotate. Think, for example, about a wrench turning a bolt.

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