ASVAB Mechanical Comprehension Practice Test 914344 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.30
Score	0%	66%

Review

1 If input effort is 100 ft⋅lb, what output effort will be produced by a machine with a mechanical advantage of 3?

79% Answer Correctly

	150ft⋅lb
	300 ft⋅lb
	600ft⋅lb
	0ft⋅lb

Solution

Mechanical advantage is the ratio of output force to input force and tells us by how many times a machine multiplies input effort. So, a machine with a mechanical advantage of 3 will multiply an input effort of 100 ft⋅lb by 3 to produce an output effort of 300 ft⋅lb.

2 If the force applied at the blue arrow over 9 ft. moves the green box 1.8 ft., what is the mechanical advantage of this lever?

56% Answer Correctly

	5
	5.5
	2
	4.5

Solution

Mechanical advantage (MA) can be calculated knowing only the distance the effort (blue arrow) moves and the distance the resistance (green box) moves. The equation is:

MA = \( \frac{E_d}{R_d} \)

where E_d is the effort distance and R_d is the resistance distance. For this problem, the equation becomes:

MA = \( \frac{9 ft.}{1.8 ft.} \) = 5

You might be wondering how having an effort distance of 5 times the resistance distance is an advantage. Remember the principle of moments. For a lever in equilibrium the effort torque equals the resistance torque. Because torque is force x distance, if the effort distance is 5 times the resistance distance, the effort force must be \( \frac{1}{5} \) the resistance force. You're trading moving 5 times the distance for only having to use \( \frac{1}{5} \) the force.

3 The radius of the axle is 7, the radius of the wheel is 12, and the blue box weighs 55 lbs. What is the effort force necessary to balance the load?

53% Answer Correctly

	8.71 lbs.
	12 lbs.
	32.16 lbs.
	19 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 12 and the output radius (where the resistance is being applied) is 7 for a mechanical advantage of \( \frac{12}{7} \) = 1.71

MA = \( \frac{load}{effort} \) so effort = \( \frac{load}{MA} \) = \( \frac{55 lbs.}{1.71} \) = 32.16 lbs.

The steering wheel of a car is an example of which type of simple machine?

89% Answer Correctly

	first-class lever
	fixed pulley
	wheel and axle
	block and tackle

Solution

A wheel and axle uses two different diameter wheels mounted to a connecting axle. Force is applied to the larger wheel and large movements of this wheel result in small movements in the smaller wheel. Because a larger movement distance is being translated to a smaller distance, force is increased with a mechanical advantage equal to the ratio of the diameters of the wheels. An example of a wheel and axle is the steering wheel of a car.

Which class of lever is used to increase force on an object in the same direction as the force is applied?

52% Answer Correctly

	first
	second
	third
	all of these

Solution

A second-class lever is used to increase force on an object in the same direction as the force is applied. This lever requires a smaller force to lift a larger load but the force must be applied over a greater distance. The fulcrum is placed at one end of the lever and mechanical advantage increases as the object being lifted is moved closer to the fulcrum or the length of the lever is increased. An example of a second-class lever is a wheelbarrow.