ASVAB Mechanical Comprehension Practice Test 520141 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.05
Score	0%	61%

Review

1 How much work can a 1 hp engine do in 4 seconds?

52% Answer Correctly

	0 ft⋅lb
	2200 ft⋅lb
	2 ft⋅lb
	4 ft⋅lb

Solution

Horsepower (hp) is a common measure of power output for complex machines. By definition, a 1 hp machine does 550 ft⋅lb of work in 1 second: 1 hp = 550 ft⋅lb/s. Substituting the variables for this problem gives us:
\( W = 1 hp \times 550 \frac{ft⋅lb}{s} \times 4s = 2200 ft⋅lb \)

The force required to initally get an object moving is __________ the force required to keep it moving.

76% Answer Correctly

	opposite
	higher than
	lower than
	the same as

Solution

For any given surface, the coefficient of static friction is higher than the coefficient of kinetic friction. More force is required to initally get an object moving than is required to keep it moving. Additionally, static friction only arises in response to an attempt to move an object (overcome the normal force between it and the surface).

3 How much resistance could a 135 lb. effort force lift using a block and tackle pulley that has 6 ropes supporting the resistance?

81% Answer Correctly

	729 lbs.
	1620 lbs.
	812 lbs.
	810 lbs.

Solution

The mechanical advantage (MA) of a block and tackle pulley is equal to the number of times the effort force changes direction. An easy way to count how many times the effort force changes direction is to count the number of ropes that support the resistance which, in this problem, is 6. With a MA of 6, a 135 lbs. effort force could lift 135 lbs. x 6 = 810 lbs. resistance.

The principle of conservation of mechanical energy states that, as long as no other forces are applied, what will remain constant as an object falls?

45% Answer Correctly

	kinetic energy
	acceleration
	potential energy
	total mechanical energy

Solution

As an object falls, its potential energy is converted into kinetic energy. The principle of conservation of mechanical energy states that, as long as no other forces are applied, total mechanical energy (PE + KE) of the object will remain constant at all points in its descent.

Which class of lever is used to increase force on an object in the same direction as the force is applied?

52% Answer Correctly

	first
	second
	all of these
	third

Solution

A second-class lever is used to increase force on an object in the same direction as the force is applied. This lever requires a smaller force to lift a larger load but the force must be applied over a greater distance. The fulcrum is placed at one end of the lever and mechanical advantage increases as the object being lifted is moved closer to the fulcrum or the length of the lever is increased. An example of a second-class lever is a wheelbarrow.