ASVAB Mechanical Comprehension Practice Test 394793 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.06
Score	0%	61%

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

What is work?

60% Answer Correctly

	Force per unit distance
	The movement of an object by a force
	Force per unit time
	The potential for exertion

Solution

Work is accomplished when force is applied to an object: W = Fd where F is force in newtons (N) and d is distance in meters (m). Thus, the more force that must be applied to move an object, the more work is done and the farther an object is moved by exerting force, the more work is done. By definition, work is the displacement of an object resulting from applied force.

3 If you have a gear train with two gears, the first with 24 teeth and the second with 8 teeth, how many revolutions does the second gear make for each revolution of the first gear?

77% Answer Correctly

	3
	6
	2.7
	3.3

Solution

The gear ratio (V_r) of a gear train 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 only two gears so the equation becomes:

V_r = \( \frac{N_1}{N_2} \) = \( \frac{24}{8} \) = 3

4 If the green box weighs 30 lbs. and 20 lbs. of force is applied 3 ft. from the fulcrum at the blue arrow, how far from the fulcrum would the green box need to be placed to balance the lever?

55% Answer Correctly

	2 ft.
	8 ft.
	0.5 ft.
	0 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_a, our missing value, and plugging in our variables yields:

d_a = \( \frac{R_bd_b}{R_a} \) = \( \frac{20 lbs. \times 3 ft.}{30 lbs.} \) = \( \frac{60 ft⋅lb}{30 lbs.} \) = 2 ft.

What's the first gear in a gear train called?

57% Answer Correctly

	driven gear
	driver gear
	idler gear
	input gear

Solution

A gear train is two or more gears linked together. Gear trains are designed to increase or reduce the speed or torque outpout of a rotating system or change the direction of its output. The first gear in the chain is called the driver and the last gear in the chain the driven gear with the gears between them called idler gears.