ASVAB Mechanical Comprehension Practice Test 162126 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.96
Score	0%	59%

Review

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

61% Answer Correctly

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

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

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

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.

3 If the handles of a wheelbarrow are 2.0 ft. from the wheel axle, how many pounds of force must you exert to lift the handles if it's carrying a 250 lbs. load concentrated at a point 1.5 ft. from the axle?

52% Answer Correctly

	187.5
	76
	164.2
	500

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:
\( F_e = \frac{F_r d_r}{d_e} \)
\( F_e = \frac{250 \times 1.5}{2.0} \)
\( F_e = \frac{375.0}{2.0} \)
\( F_e = 187.5 \)

Which class of lever offers no mechanical advantage?

45% Answer Correctly

	third
	first
	none of these, all levers offer mechanical advantage
	second

Solution

A third-class lever is used to increase distance traveled by an object in the same direction as the force applied. The fulcrum is at one end of the lever, the object at the other, and the force is applied between them. This lever does not impart a mechanical advantage as the effort force must be greater than the load but does impart extra speed to the load. Examples of third-class levers are shovels and tweezers.

Which of the following surfaces would have the lowest coefficient of friction?

85% Answer Correctly

	tile
	concrete
	ice
	leather

Solution

Coefficient of friction (μ) represents how much two materials resist sliding across each other. Smooth surfaces like ice have low coefficients of friction while rough surfaces like concrete have high μ.