ASVAB Mechanical Comprehension Practice Test 592039 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.58
Score	0%	52%

Review

Which class of lever offers no mechanical advantage?

45% Answer Correctly

	third
	first
	second
	none of these, all levers offer mechanical advantage

Solution

A third-class lever is used to increase distance traveled by an object in the same direction as the force applied. The fulcrum is at one end of the lever, the object at the other, and the force is applied between them. This lever does not impart a mechanical advantage as the effort force must be greater than the load but does impart extra speed to the load. Examples of third-class levers are shovels and tweezers.

2 What is the power output of a 3 hp engine that's 80% efficient?

40% Answer Correctly

	0 \( \frac{ft⋅lb}{s} \)
	240 \( \frac{ft⋅lb}{s} \)
	1320 \( \frac{ft⋅lb}{s} \)
	3960 \( \frac{ft⋅lb}{s} \)

Solution

\( Efficiency = \frac{Power_{out}}{Power_{in}} \times 100 \)
Solving for power out: \( P_{o} = \frac{E \times P_{i}}{100} \)
Knowing that 1 hp = 550 \( \frac{ft⋅lb}{s} \), P_i becomes 3 hp x 550 \( \frac{ft⋅lb}{s} \) = 1650 \( \frac{ft⋅lb}{s} \)
\( P_{o} = \frac{E \times P_{i}}{100} = \frac{80 \times 1650 \frac{ft⋅lb}{s}}{100} \) \( = \frac{132000 \frac{ft⋅lb}{s}}{100} \) = 1320 \( \frac{ft⋅lb}{s} \)

Which of the following is not true of a first-class lever?

51% Answer Correctly

	changes the direction of force
	decreases distance
	increases force
	increases distance

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.

The mechanical advantage of a block and tackle is equal to which of the following?

69% Answer Correctly

	the number of connecting ropes
	the number of loads
	the number of input forces
	the number of pulleys

Solution

Two or more pulleys used together constitute a block and tackle which, unlike a fixed pulley, does impart mechanical advantage as a function of the number of pulleys that make up the arrangement. So, for example, a block and tackle with three pulleys would have a mechanical advantage of three.

5 How much work can a 9 hp engine do in 4 seconds?

52% Answer Correctly

	36 ft⋅lb
	0 ft⋅lb
	2 ft⋅lb
	19800 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:
\( W = 9 hp \times 550 \frac{ft⋅lb}{s} \times 4s = 19800 ft⋅lb \)