ASVAB Mechanical Comprehension Practice Test 757578 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.94
Score	0%	59%

Review

Which of the following is the formula for hydraulic pressure?

58% Answer Correctly

	P = FA²
	P = F/A²
	P = FA
	P = F/A

Solution

Hydraulics is the transmission of force through the use of liquids. Liquids are especially suited for transferring force in complex machines because they compress very little and can occupy very small spaces. Hydraulic pressure is calculated by dividing force by the area over which it is applied: P = F/A where F is force in pounds, A is area in square inches, and the resulting pressure is in pounds per square inch (psi).

A fixed pulley has a mechanical advantage of:

68% Answer Correctly

	1
	-1
	0
	2

Solution

A fixed pulley is used to change the direction of a force and does not multiply the force applied. As such, it has a mechanical advantage of one. The benefit of a fixed pulley is that it can allow the force to be applied at a more convenient angle, for example, pulling downward or horizontally to lift an object instead of upward.

Sam can do 50 ft. lb. of work in 2 minutes and 5 seconds. What would Sam have to do to increase his power output?

64% Answer Correctly

	do the work in 3 minutes
	do 100 ft. lb. of work in 4 minutes 12 seconds
	do the work in 2 minutes
	do 25 ft. lb. of work in 2 minutes 5 seconds

Solution

Power is the rate of doing work or \(\frac{W}{t}\). To increase power, increase the work being done in the same amount of time or do the same amount of work in less time.

4 If the green box weighs 25 lbs. and is 9 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 8 ft.?

63% Answer Correctly

	3 lbs.
	28.13 lbs.
	9.38 lbs.
	200 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:

R_ad_a = R_bd_b

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 R_b, our missing value, and plugging in our variables yields:

R_b = \( \frac{R_ad_a}{d_b} \) = \( \frac{25 lbs. \times 9 ft.}{8 ft.} \) = \( \frac{225 ft⋅lb}{8 ft.} \) = 28.13 lbs.

5 What is the power output of a 4 hp engine that's 25% efficient?

40% Answer Correctly

	550 \( \frac{ft⋅lb}{s} \)
	100 \( \frac{ft⋅lb}{s} \)
	2200 \( \frac{ft⋅lb}{s} \)
	137.5 \( \frac{ft⋅lb}{s} \)

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 4 hp x 550 \( \frac{ft⋅lb}{s} \) = 2200 \( \frac{ft⋅lb}{s} \)
\( P_{o} = \frac{E \times P_{i}}{100} = \frac{25 \times 2200 \frac{ft⋅lb}{s}}{100} \) \( = \frac{55000 \frac{ft⋅lb}{s}}{100} \) = 550 \( \frac{ft⋅lb}{s} \)