ASVAB Mechanical Comprehension Practice Test 697558 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.20
Score	0%	64%

Review

1 If the green arrow in this diagram represents 450 ft⋅lb of work, how far will the box move if it weighs 150 pounds?

73% Answer Correctly

	0 ft.
	50 ft.
	3 ft.
	6 ft.

Solution

The Law of Work states that the work put into a machine is equal to the work received from the machine under ideal conditions. In equation form, that's:

W_in = W_out
F_effort x d_effort = F_resistance x d_resistance

In this problem, the effort work is 450 ft⋅lb and the resistance force is 150 lbs. and we need to calculate the resistance distance:

W_in = F_resistance x d_resistance
450 ft⋅lb = 150 lbs. x d_resistance
d_resistance = \( \frac{450ft⋅lb}{150 lbs.} \) = 3 ft.

2 If the green box is 7 ft. from the fulcrum and a certain force applied 5 ft. from the fulcrum at the blue arrow balances the lever, what is the mechanical advantage?

61% Answer Correctly

	0.71
	2.14
	1.07
	-5.29

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 = \( \frac{E_a}{R_a} \) = \( \frac{5 ft.}{7 ft.} \) = 0.71

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.

Connected gears of different numbers of teeth are used together to change which of the following charasteristics of the input force?

66% Answer Correctly

	energy
	force
	torque
	rotational direction

Solution

Connected gears of different numbers of teeth are used together to change the rotational speed and torque of the input force. If the smaller gear drives the larger gear, the speed of rotation will be reduced and the torque will increase. If the larger gear drives the smaller gear, the speed of rotation will increase and the torque will be reduced.

Concurrent forces:

55% Answer Correctly

	act in a common dimension
	pass through a common point
	act along the same line of action
	act in a common plane

Solution

Collinear forces act along the same line of action, concurrent forces pass through a common point and coplanar forces act in a common plane.

According to Boyle's law, for a fixed amount of gas kept at a fixed temperature, which of the following are inversely proportional?

64% Answer Correctly

	volume, mass
	pressure, density
	pressure, volume
	density, volume

Solution

Boyle's law states that "for a fixed amount of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional".