ASVAB Mechanical Comprehension Practice Test 530797 Results

Your Results Global Average
Questions 5 5
Correct 0 3.49
Score 0% 70%

Review

1 If the green box weighs 5 lbs. and is 7 ft. from the fulcrum, how much weight would need to be placed at the blue arrow to balance the lever if the arrow's distance from the fulcrum is 6 ft.?
63% Answer Correctly
5.83 lbs.
11.67 lbs.
1 lbs.
30 lbs.
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 Rb, our missing value, and plugging in our variables yields:

Rb = \( \frac{R_ad_a}{d_b} \) = \( \frac{5 lbs. \times 7 ft.}{6 ft.} \) = \( \frac{35 ft⋅lb}{6 ft.} \) = 5.83 lbs.

2

Concurrent forces:

55% Answer Correctly

pass through a common point

act in a common plane

act along the same line of action

act in a common dimension
Solution

Collinear forces act along the same line of action, concurrent forces pass through a common point and coplanar forces act in a common plane.

3 What is the efficiency of a machine has work input of 235 ft⋅lb and work output of 223 ft⋅lb?
68% Answer Correctly
0%
95%
1%
190%
Solution
Due to friction, a machine will never be able to utilize 100% of its work input. A certain percentage of that input will be lost in overcoming friction within the machine. Effeciency is a measure of how much of a machine's work input can be turned into useful work output and is calculated by dividing work output by work input and multiplying the result by 100:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{223 ft⋅lb}{235 ft⋅lb} \times 100 \) \( = 95% \) %
4

The force amplification achieved by using a tool, mechanical device or machine system is called:

80% Answer Correctly

work

efficiency

mechanical advantage

power
Solution

Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. Such a device utilizes input force and trades off forces against movement to amplify and/or change its direction.

5

Friction resists movement in a direction __________ to the movement.

82% Answer Correctly

opposite

normal

perpendicular

parallel
Solution

Friction resists movement. Kinetic (also called sliding or dynamic) friction resists movement in a direction opposite to the movement. Because it opposes movement, kinetic friction will eventually bring an object to a stop. An example is a rock that's sliding across ice.