ASVAB Mechanical Comprehension Practice Test 142036 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.93
Score	0%	59%

Review

1 A 280 lb. barrel is rolled up a 7 ft. ramp to a platform that's 3 ft. tall. What effort is required to move the barrel?

53% Answer Correctly

	120 lbs.
	60 lbs.
	180 lbs.
	240 lbs.

Solution

This problem describes an inclined plane and, for an inclined plane, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance:

F_ed_e = F_rd_r

Plugging in the variables from this problem yields:

F_e x 7 ft. = 280 lbs. x 3 ft.
F_e = \( \frac{840 ft⋅lb}{7 ft.} \) = 120 lbs.

2 If the green box weighs 25 lbs. and is 5 ft. from the fulcrum, how much force would need to be applied at the blue arrow to balance the lever if the arrow's distance from the fulcrum is 8 ft.?

62% Answer Correctly

	15.63 lbs.
	200 lbs.
	3.91 lbs.
	5.21 lbs.

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 R_b, our missing value, and plugging in our variables yields:

R_b = \( \frac{R_ad_a}{d_b} \) = \( \frac{25 lbs. \times 5 ft.}{8 ft.} \) = \( \frac{125 ft⋅lb}{8 ft.} \) = 15.63 lbs.

Torque involves a perpendicular force applied to a lever arm that moves around a center of rotation. Increasing the length of the lever arm will do which of the following?

54% Answer Correctly

	decrease applied force
	decrease torque
	increase torque
	increase applied force

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).

4 If the handles of a wheelbarrow are 2.5 ft. from the wheel axle, how many pounds of force must you exert to lift the handles if it's carrying a 210 lbs. load concentrated at a point 1.0 ft. from the axle?

52% Answer Correctly

	525
	75.8
	142.8
	84

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 effort force:
\( F_e = \frac{F_r d_r}{d_e} \)
\( F_e = \frac{210 \times 1.0}{2.5} \)
\( F_e = \frac{210.0}{2.5} \)
\( F_e = 84 \)

Two or more pulleys used together are called:

71% Answer Correctly

	wheel and axle
	block and tackle
	third-class lever
	gears

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.