ASVAB Mechanical Comprehension Practice Test 192829 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.31
Score	0%	66%

Review

Which of the following is the formula for torque?

61% Answer Correctly

	τ = F/r²
	τ = r/F
	τ = rF
	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).

2 If you lift a 31 lbs. rock 6 ft. from the ground, how much work have you done?

70% Answer Correctly

	372 ft⋅lb
	0 ft⋅lb
	186 ft⋅lb
	37 ft⋅lb

Solution

Work is force times distance. In this case, the force is the weight of the rock so:
\( W = F \times d \)
\( W = 31 \times 6 \)
\( W = 186 \)

3 How much resistance could a 40 lb. effort force lift using a block and tackle pulley that has 6 ropes supporting the resistance?

81% Answer Correctly

	720 lbs.
	120 lbs.
	240 lbs.
	239 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 6. With a MA of 6, a 40 lbs. effort force could lift 40 lbs. x 6 = 240 lbs. resistance.

4 What is the efficiency of a machine has work input of 160 ft⋅lb and work output of 136 ft⋅lb?

67% Answer Correctly

	0%
	85%
	170%
	21%

Solution

Due to friction, a machine will never be able to utilize 100% of its work input. A certain percentage of that input will be lost in overcoming friction within the machine. Effeciency is a measure of how much of a machine's work input can be turned into useful work output and is calculated by dividing work output by work input and multiplying the result by 100:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{136 ft⋅lb}{160 ft⋅lb} \times 100 \) \( = 85% \) %

A fixed pulley is useful for which of the following?

53% Answer Correctly

	multiplying the input distance
	multiplying the input force
	changing the direction of the input force
	changing the direction of the output force

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.