ASVAB Mechanical Comprehension Practice Test 454919 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.98
Score	0%	60%

Review

The principle of moments defines equilibrium in terms of:

54% Answer Correctly

	speed
	power
	energy
	torque

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.

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

59% Answer Correctly

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

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.

3 If the green box is 8 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

	0.38
	5.25
	0.23
	0.25

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 = \( \frac{E_a}{R_a} \) = \( \frac{2 ft.}{8 ft.} \) = 0.25

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.

4 If you lift a 27 lbs. rock 21 ft. from the ground, how much work have you done?

72% Answer Correctly

	273 ft⋅lb
	567 ft⋅lb
	1 ft⋅lb
	1134 ft⋅lb

Solution

Work is force times distance. In this case, the force is the weight of the rock so:
\( W = F \times d \)
\( W = 27 \times 21 \)
\( W = 567 \)

Assuming force applied remains constant, which of the following will result in more work being done?

53% Answer Correctly

	moving the object farther
	increasing the coefficient of friction
	moving the object with more speed
	moving the object with more acceleration

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.