ASVAB Mechanical Comprehension Practice Test 520444 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.09
Score	0%	62%

Review

Which of the following represents the force a surface exerts when an object presses against it?

48% Answer Correctly

	friction
	mass
	counter force
	normal force

Solution

Normal force (F_N) represents the force a surface exerts when an object presses against it.

2 How much resistance could a 100 lb. effort force lift using a block and tackle pulley that has 4 ropes supporting the resistance?

81% Answer Correctly

	1200 lbs.
	440 lbs.
	400 lbs.
	394 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 4. With a MA of 4, a 100 lbs. effort force could lift 100 lbs. x 4 = 400 lbs. resistance.

3 If A = 11 ft., B = 1 ft., C = 9 ft., the green box weighs 25 lbs. and the blue box weighs 30 lbs., what does the orange box have to weigh for this lever to balance?

44% Answer Correctly

	27.22 lbs.
	54.44 lbs.
	2 lbs.
	9.07 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:

25 lbs. x 11 ft. = 30 lbs. x 1 ft. + f_C x 9 ft.

275 ft. lbs. = 30 ft. lbs. + f_C x 9 ft.

f_C = \( \frac{275 ft. lbs. - 30 ft. lbs.}{9 ft.} \) = \( \frac{245 ft. lbs.}{9 ft.} \) = 27.22 lbs.

A block and tackle with four pulleys would have a mechanical advantage of:

79% Answer Correctly

	4
	2
	0
	1

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.

For a hydraulic system, pressure applied to the input of the system will increase the pressure in which parts of the system?

58% Answer Correctly

	the portions of the system at an altitude above the input
	all of these are correct
	the portions of the system at an altitude below the input
	everywhere in the system

Solution

Pascal's law states that a pressure change occurring anywhere in a confined incompressible fluid is transmitted throughout the fluid such that the same change occurs everywhere. For a hydraulic system, this means that a pressure applied to the input of the system will increase the pressure everywhere in the system.