ASVAB Mechanical Comprehension Practice Test 407819 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.29
Score	0%	66%

Review

1 How much resistance could a 230 lb. effort force lift using a block and tackle pulley that has 4 ropes supporting the resistance?

81% Answer Correctly

	1840 lbs.
	828 lbs.
	306 lbs.
	920 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 230 lbs. effort force could lift 230 lbs. x 4 = 920 lbs. resistance.

The mass of an object correlates to the size of the object but ultimately depends on:

67% Answer Correctly

	the object's density
	the object's weight
	gravity
	the object's potential energy

Solution

Mass is a measure of the amount of matter in an object. In general, larger objects have larger mass than smaller objects but mass ultimately depends on how compact (dense) a substance is.

3 If the handles of a wheelbarrow are 2.0 ft. from the wheel axle and the load is concentrated at a point 1.5 ft. from the axle, how many pounds of load will a 180 lbs. force lift?

47% Answer Correctly

	87.7
	360
	135
	240

Solution

This problem describes a second-class lever and, for a second class lever, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance: F_ed_e = F_rd_r. In this problem we're looking for resistance force:
\( F_r = \frac{F_e d_e}{d_r} \)
\( F_r = \frac{180 \times 2.0}{1.5} \)
\( F_r = \frac{360.0}{1.5} \)
\( F_r = 240 \)

4 If the green box weighs 60 lbs. and is 5 ft. from the fulcrum, how far from the fulcrum would a 5 lbs. force need to be applied to balance the lever?

58% Answer Correctly

	300 ft.
	0 ft.
	180 ft.
	60 ft.

Solution

To balance this lever the torques at the green box and the blue arrow 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 green box and b the blue arrow, R is resistance (weight/force) and d is the distance from the fulcrum.

Solving for d_b, our missing value, and plugging in our variables yields:

d_b = \( \frac{R_ad_a}{R_b} \) = \( \frac{60 lbs. \times 5 ft.}{5 lbs.} \) = \( \frac{300 ft⋅lb}{5 lbs.} \) = 60 ft.

Hydraulics is the transmission of force through the use of which of the following?

74% Answer Correctly

	air pressure
	torque
	gear systems
	liquids

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).