ASVAB Mechanical Comprehension Practice Test 287445 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.06
Score	0%	61%

Review

1 What is the mechanical advantage of this inclined plane if the length of the ramp is 64 ft. and the height of the green box is 8 ft.?

82% Answer Correctly

	8
	10
	-1
	24

Solution

The mechanical advantage (MA) of an inclined plane is the effort distance divided by the resistance distance. In this case, the effort distance is the length of the ramp and the resistance distance is the height of the green box:

MA = \( \frac{d_e}{d_r} \) = \( \frac{64 ft.}{8 ft.} \) = 8

A watt is the unit for which of the following?

71% Answer Correctly

	work
	mechanical advantage
	energy
	power

Solution

Power is the rate at which work is done, P = w/t, or work per unit time. The watt (W) is the unit for power and is equal to 1 joule (or newton-meter) per second. Horsepower (hp) is another familiar unit of power used primarily for rating internal combustion engines. 1 hp equals 746 watts.

3 What is the power output of a 9 hp engine that's 50% efficient?

40% Answer Correctly

	450 \( \frac{ft⋅lb}{s} \)
	9900 \( \frac{ft⋅lb}{s} \)
	0 \( \frac{ft⋅lb}{s} \)
	2475 \( \frac{ft⋅lb}{s} \)

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 9 hp x 550 \( \frac{ft⋅lb}{s} \) = 4950 \( \frac{ft⋅lb}{s} \)
\( P_{o} = \frac{E \times P_{i}}{100} = \frac{50 \times 4950 \frac{ft⋅lb}{s}}{100} \) \( = \frac{247500 \frac{ft⋅lb}{s}}{100} \) = 2475 \( \frac{ft⋅lb}{s} \)

A wedge converts force applied to its blunt end into force __________ its inclined surface.

57% Answer Correctly

	opposite to
	parallel to
	along
	perpendicular to

Solution

The wedge is a moving inclined plane that is used to lift, hold, or break apart an object. A wedge converts force applied to its blunt end into force perpendicular to its inclined surface. In contrast to a stationary plane where force is applied to the object being moved, with a wedge the object is stationary and the force is being applied to the plane. Examples of a wedge include knives and chisels.

Which of the following will increase the mechanical advantage of a second-class lever?

55% Answer Correctly

	decrease the length of the lever
	move the fulcrum between the force and the object being lifted
	move the object being lifted farther away from the fulcrum
	move the object being lifted closer to the fulcrum

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.