ASVAB Mechanical Comprehension Practice Test 493885 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.71
Score	0%	54%

Review

1 If the handles of a wheelbarrow are 0.5 ft. from the wheel axle, how many pounds of force must you exert to lift the handles if it's carrying a 200 lbs. load concentrated at a point 0.5 ft. from the axle?

52% Answer Correctly

	0
	None of these is correct
	331.6
	200

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:
\( F_e = \frac{F_r d_r}{d_e} \)
\( F_e = \frac{200 \times 0.5}{0.5} \)
\( F_e = \frac{100.0}{0.5} \)
\( F_e = 200 \)

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
	increase torque
	increase applied force
	decrease torque

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).

Two gears are connected and the smaller gear drives the larger gear. The speed of rotation will __________ and the torque will __________.

61% Answer Correctly

	decrease, increase
	increase, increase
	increase, decrease
	decrease, decrease

Solution

Connected gears of different numbers of teeth are used together to change the rotational speed and torque of the input force. If the smaller gear drives the larger gear, the speed of rotation will be reduced and the torque will increase. If the larger gear drives the smaller gear, the speed of rotation will increase and the torque will be reduced.

A screw is most like which of the following other simple machines?

50% Answer Correctly

	first-class lever
	block and tackle
	inclined plane
	wheel and axle

Solution

A screw is an inclined plane wrapped in ridges (threads) around a cylinder. The distance between these ridges defines the pitch of the screw and this distance is how far the screw advances when it is turned once. The mechanical advantage of a screw is its circumference divided by the pitch.

5 A 440 lb. barrel is rolled up a 17 ft. ramp to a platform that's 2 ft. tall. What effort is required to move the barrel?

53% Answer Correctly

	56.9 lbs.
	51.8 lbs.
	54.8 lbs.
	17.3 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 17 ft. = 440 lbs. x 2 ft.
F_e = \( \frac{880 ft⋅lb}{17 ft.} \) = 51.8 lbs.