ASVAB Mechanical Comprehension Practice Test 119811 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.36
Score	0%	67%

Review

1 What's the mechanical advantage of a wedge that's 2 inches wide and 8 inches long?

83% Answer Correctly

	7
	4
	2
	0

Solution

The mechanical advantage (MA) of a wedge is its length divided by its thickness:

MA = \( \frac{l}{t} \) = \( \frac{8 in.}{2 in.} \) = 4

A box is resting on a smooth floor. Static friction is present:

59% Answer Correctly

	if the coefficient of friction is greater than one
	at all times
	only if normal force is present
	when an attempt is made to move the box

Solution

For any given surface, the coefficient of static friction is higher than the coefficient of kinetic friction. More force is required to initally get an object moving than is required to keep it moving. Additionally, static friction only arises in response to an attempt to move an object (overcome the normal force between it and the surface).

3 The green box weighs 75 lbs. and a 60 lbs. weight is placed 1 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?

57% Answer Correctly

	0.8 ft.
	2.4 ft.
	3.2 ft.
	0.27 ft.

Solution

To balance this lever the torques on each side of the fulcrum 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 left side of the fulcrum and b the right, R is resistance (weight) and d is the distance from the fulcrum.

Solving for d_a, our missing value, and plugging in our variables yields:

d_a = \( \frac{R_bd_b}{R_a} \) = \( \frac{60 lbs. \times 1 ft.}{75 lbs.} \) = \( \frac{60 ft⋅lb}{75 lbs.} \) = 0.8 ft.

What is work?

60% Answer Correctly

	The movement of an object by a force
	Force per unit distance
	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.

5 If you have a gear train with two gears, the first with 20 teeth and the second with 4 teeth, how many revolutions does the second gear make for each revolution of the first gear?

78% Answer Correctly

	7
	10
	2.5
	5

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 = \( \frac{N_1}{N_2} \) = \( \frac{20}{4} \) = 5