ASVAB Mechanical Comprehension Practice Test 183583 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.95
Score	0%	59%

Review

The principle of moments defines equilibrium in terms of:

53% Answer Correctly

	speed
	energy
	torque
	power

Solution

According to the principle of moments, you can maintain equilibrium if the moments (forces) tending to clockwise rotation are equal to the moments tending to counterclockwise rotation. Another name for these moments of force is torque.

2 If the green box is 9 ft. from the fulcrum and a certain force applied 2 ft. from the fulcrum at the blue arrow balances the lever, what is the mechanical advantage?

61% Answer Correctly

	0.67
	0.22
	0.33
	0.07

Solution

Because this lever is in equilibrium, we know that the effort force at the blue arrow is equal to the resistance weight of the green box. For a lever that's in equilibrium, one method of calculating mechanical advantage (MA) is to divide the length of the effort arm (E_a) by the length of the resistance arm (R_a):

MA = \( \frac{E_a}{R_a} \) = \( \frac{2 ft.}{9 ft.} \) = 0.22

When a lever is in equilibrium, the torque from the effort and the resistance are equal. The equation for equilibrium is R_ad_a = R_bd_b where a and b are the two points at which effort/resistance is being applied to the lever.

In this problem, R_a and R_b are such that the lever is in equilibrium meaning that some multiple of the weight of the green box is being applied at the blue arrow. For a lever, this multiple is a function of the ratio of the distances of the box and the arrow from the fulcrum. That's why, for a lever in equilibrium, only the distances from the fulcrum are necessary to calculate mechanical advantage.

If the lever were not in equilibrium, you would first have to calculate the forces and distances necessary to put it in equilibrium and then divide E_a by R_a to get the mechanical advantage.

A fixed pulley has a mechanical advantage of:

68% Answer Correctly

	2
	0
	1
	-1

Solution

A fixed pulley is used to change the direction of a force and does not multiply the force applied. As such, it has a mechanical advantage of one. The benefit of a fixed pulley is that it can allow the force to be applied at a more convenient angle, for example, pulling downward or horizontally to lift an object instead of upward.

What is work?

60% Answer Correctly

	Force per unit time
	Force per unit distance
	The movement of an object by a force
	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 The radius of the axle is 7, the radius of the wheel is 10, and the blue box weighs 85 lbs. What is the effort force necessary to balance the load?

53% Answer Correctly

	10.01 lbs.
	59.44 lbs.
	14.3 lbs.
	7 lbs.

Solution

The mechanical advantage of a wheel and axle is the input radius divided by the output radius:

MA = \( \frac{r_i}{r_o} \)

In this case, the input radius (where the effort force is being applied) is 10 and the output radius (where the resistance is being applied) is 7 for a mechanical advantage of \( \frac{10}{7} \) = 1.43

MA = \( \frac{load}{effort} \) so effort = \( \frac{load}{MA} \) = \( \frac{85 lbs.}{1.43} \) = 59.44 lbs.