ASVAB Mechanical Comprehension Practice Test 38980 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.78
Score	0%	56%

Review

1 If A = 12 ft., B = 3 ft., C = 8 ft., the green box weighs 45 lbs. and the blue box weighs 50 lbs., what does the orange box have to weigh for this lever to balance?

44% Answer Correctly

	16.25 lbs.
	0 lbs.
	15 lbs.
	48.75 lbs.

Solution

In order for this lever to balance, the torque acting on each side of the fulrum must be equal. So, the torque produced by A must equal the torque produced by B and C. Torque is weight x distance from the fulcrum which means that the following must be true for the lever to balance:

f_Ad_A = f_Bd_B + f_Cd_C

For this problem, this equation becomes:

45 lbs. x 12 ft. = 50 lbs. x 3 ft. + f_C x 8 ft.

540 ft. lbs. = 150 ft. lbs. + f_C x 8 ft.

f_C = \( \frac{540 ft. lbs. - 150 ft. lbs.}{8 ft.} \) = \( \frac{390 ft. lbs.}{8 ft.} \) = 48.75 lbs.

Which of the following represents how much two materials resist sliding across each other?

53% Answer Correctly

	normal friction
	kinetic friction
	coefficient of friction
	static friction

Solution

Coefficient of friction (μ) represents how much two materials resist sliding across each other. Smooth surfaces like ice have low coefficients of friction while rough surfaces like concrete have high μ.

Which of the following is the formula for torque?

61% Answer Correctly

	τ = rF
	τ = r/F
	τ = F/r²
	τ = F/r

Solution

Torque measures force applied during rotation: τ = rF. Torque (τ, the Greek letter tau) = the radius of the lever arm (r) multiplied by the force (F) applied. Radius is measured from the center of rotation or fulcrum to the point at which the perpendicular force is being applied. The resulting unit for torque is newton-meter (N-m) or foot-pound (ft-lb).

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?

63% Answer Correctly

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

A shovel is an example of which class of lever?

56% Answer Correctly

	second
	third
	first
	a shovel is not a lever

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.