ASVAB Mechanical Comprehension Practice Test 817124 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.85
Score	0%	57%

Review

If the handles of a wheelbarrow are 3 ft. from the wheel axle, what force must you exert to lift the handles if it's carrying a 270 lb. load concentrated at a point 0.5 ft. from the axle?

56% Answer Correctly

	90 lbs
	45 lbs
	0.83 lbs
	810 lbs

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. Plugging in the variables from this problem yields:

F_e x 3 ft. = 270 lbs x 0.5 ft
F_e = 135 ft-lb. / 3 ft
F_e= 45 lbs

Which of the following will increase the mechanical advantage of this inclined plane?

59% Answer Correctly

	shorten the ramp
	lengthen the ramp
	lower the force acting at the blue arrow
	increase the force acting at the blue arrow

Solution

The mechanical advantage (MA) of an inclined plane is the effort distance divided by the resistance distance. In order to increase mechanical advantage, this ratio must increase which means making the effort distance longer and this can be accomplished by lengthening the length of the ramp.

A wedge converts force applied to its blunt end into force __________ its inclined surface.

57% Answer Correctly

	parallel to
	opposite to
	perpendicular to
	along

Solution

The wedge is a moving inclined plane that is used to lift, hold, or break apart an object. A wedge converts force applied to its blunt end into force perpendicular to its inclined surface. In contrast to a stationary plane where force is applied to the object being moved, with a wedge the object is stationary and the force is being applied to the plane. Examples of a wedge include knives and chisels.

4 If you have a gear train with three gears, the first with 24 teeth, the second with 14 teeth, and the third with 2 teeth, what is its mechanical advantage?

51% Answer Correctly

	13.5
	12
	6
	24

Solution

The mechanical advantage of a gear train is its gear ratio. The gear ratio (V_r) is the product of the gear ratios between the pairs of meshed gears. Let N represent the number of teeth for each gear:

V_r = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) \( \frac{N_3}{N_4} \) ... \( \frac{N_n}{N_{n+1}} \)

In this problem, we have three gears so the equation becomes:

V_r = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) = \( \frac{24}{14} \) \( \frac{14}{2} \) = \( \frac{24}{2} \) = 12

Which of the following is the formula for torque?

62% Answer Correctly

	τ = r/F
	τ = rF
	τ = F/r²
	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).