ASVAB Mechanical Comprehension Practice Test 587460 Results

Your Results Global Average
Questions 5 5
Correct 0 2.85
Score 0% 57%

Review

1

The measure of how much of the power put into a machine is turned into movement or force is called:

56% Answer Correctly

power

mechanical advantage

efficiency

force multiplication
Solution

The efficiency of a machine describes how much of the power put into the machine is turned into movement or force. A 100% efficient machine would turn all of the input power into output movement or force. However, no machine is 100% efficient due to friction, heat, wear and other imperfections that consume input power without delivering any output.

2

Which of the following represents how much two materials resist sliding across each other?

53% Answer Correctly

static friction

normal friction

kinetic friction

coefficient of friction
Solution

Coefficient of friction (μ) represents how much two materials resist sliding across each other.  Smooth surfaces like ice have low coefficients of friction while rough surfaces like concrete have high μ.

3

Which of the following statements about this pulley configuration is false?

48% Answer Correctly

This is a block and tackle pulley configuration

Only multiplies the effort force

Changes the direction of and multiplies the effort force

Mechanical advantage is the number of ropes that support the resistance
Solution

A block and tackle is a combination of one or more fixed pulleys and one or more movable pulleys where the fixed pulleys change the direction of the effort force and the movable pulleys multiply it. The mechanical advantage is equal to the number of times the effort force changes direction and can be increased by adding more pulley wheels to the system. An easy way to find the mechanical advantage of a block and tackle pulley system is to count the number of ropes that support the resistance.

4 If the green box weighs 35 lbs. and is 5 ft. from the fulcrum, how far from the fulcrum would a 55 lbs. weight need to be placed to balance the lever?
60% Answer Correctly
9.55 ft.
7 ft.
1.59 ft.
3.18 ft.
Solution

To balance this lever the torques on each side of the fulcrum must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:

Rada = Rbdb

where a represents the left side of the fulcrum and b the right, R is resistance (weight) and d is the distance from the fulcrum.

Solving for db, our missing value, and plugging in our variables yields:

db = \( \frac{R_ad_a}{R_b} \) = \( \frac{35 lbs. \times 5 ft.}{55 lbs.} \) = \( \frac{175 ft⋅lb}{55 lbs.} \) = 3.18 ft.

5

A a seesaw / teeter-totter is an example of which of the following?

69% Answer Correctly

inclined plane

first-class lever

second-class lever

third-class lever
Solution

A first-class lever is used to increase force or distance while changing the direction of the force. The lever pivots on a fulcrum and, when a force is applied to the lever at one side of the fulcrum, the other end moves in the opposite direction. The position of the fulcrum also defines the mechanical advantage of the lever. If the fulcrum is closer to the force being applied, the load can be moved a greater distance at the expense of requiring a greater input force. If the fulcrum is closer to the load, less force is required but the force must be applied over a longer distance. An example of a first-class lever is a seesaw / teeter-totter.