ASVAB Mechanical Comprehension Practice Test 114435 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.50
Score	0%	70%

Review

1 How much resistance could a 125 lb. effort force lift using a block and tackle pulley that has 8 ropes supporting the resistance?

80% Answer Correctly

	1000 lbs.
	333 lbs.
	3000 lbs.
	1002 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 8. With a MA of 8, a 125 lbs. effort force could lift 125 lbs. x 8 = 1000 lbs. resistance.

2 If A = 11 ft., B = 2 ft., C = 7 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

	30.71 lbs.
	2 lbs.
	0 lbs.
	122.86 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 2 ft. + f_C x 7 ft.

275 ft. lbs. = 60 ft. lbs. + f_C x 7 ft.

f_C = \( \frac{275 ft. lbs. - 60 ft. lbs.}{7 ft.} \) = \( \frac{215 ft. lbs.}{7 ft.} \) = 30.71 lbs.

Specific gravity is a comparison of the density of an object with the density of:

57% Answer Correctly

	air
	carbon
	oil
	water

Solution

Specific gravity is the ratio of the density of equal volumes of a substance and water and is measured by a hyrdometer.

An object's resistance to changes in direction is known as:

81% Answer Correctly

	kinetic energy
	inertia
	mass
	weight

Solution

The more mass a substance has the more force is required to move it or to change its direction. This resistance to changes in direction is known as inertia.

When all forces acting on a system cancel each other out, this is called:

80% Answer Correctly

	equilibrium
	rest
	stasis
	potential energy

Solution

When a system is stable or balanced (equilibrium) all forces acting on the system cancel each other out. In the case of torque, equilibrium means that the sum of the anticlockwise moments about a center of rotation equal the sum of the clockwise moments.