ASVAB Mechanical Comprehension Practice Test 889656 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.43
Score	0%	49%

Review

1 If the handles of a wheelbarrow are 2.5 ft. from the wheel axle and the load is concentrated at a point 1.5 ft. from the axle, how many pounds of load will a 260 lbs. force lift?

47% Answer Correctly

	69.3
	38.8
	99.1
	433.3

Solution

This problem describes a second-class lever and, for a second class lever, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance: F_ed_e = F_rd_r. In this problem we're looking for resistance force:
\( F_r = \frac{F_e d_e}{d_r} \)
\( F_r = \frac{260 \times 2.5}{1.5} \)
\( F_r = \frac{650.0}{1.5} \)
\( F_r = 433.3 \)

2 If the force applied at the blue arrow over 5 ft. moves the green box 1.67 ft., what is the mechanical advantage of this lever?

56% Answer Correctly

	4.5
	3
	6
	3.3

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 = \( \frac{5 ft.}{1.67 ft.} \) = 3

You might be wondering how having an effort distance of 3 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 3 times the resistance distance, the effort force must be \( \frac{1}{3} \) the resistance force. You're trading moving 3 times the distance for only having to use \( \frac{1}{3} \) the force.

Which of the following statements about drag is false?

58% Answer Correctly

	drag occurs during movement through a fluid
	the amount of drag depends on the shape of an object
	the amount of drag depends on the speed of an object
	slower objects experience more drag than faster objects

Solution

Drag is friction that opposes movement through a fluid like liquid or air. The amount of drag depends on the shape and speed of the object with slower objects experiencing less drag than faster objects and more aerodynamic objects experiencing less drag than those with a large leading surface area.

What's the last gear in a gear train called?

38% Answer Correctly

	idler gear
	driver gear
	driven gear
	output gear

Solution

A gear train is two or more gears linked together. Gear trains are designed to increase or reduce the speed or torque outpout of a rotating system or change the direction of its output. The first gear in the chain is called the driver and the last gear in the chain the driven gear with the gears between them called idler gears.

5 If this lever is in equilibrium with an effort force of 5.0 ft. lb. at the blue arrow and a resistance force of 4 ft. lb. at the green box, what is its mechanical advantage?

48% Answer Correctly

	0.88
	0.27
	2.3
	0.8

Solution

Mechanical advantage (MA) is the ratio by which effort force relates to resistance force. If both forces are known, calculating MA is simply a matter of dividing resistance force by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{4 ft.}{5.0 ft.} \) = 0.8

In this case, the mechanical advantage is less than one meaning that each unit of effort force results in just 0.8 units of resistance force. However, a third class lever like this isn't designed to multiply force like a first class lever. A third class lever is designed to multiply distance and speed at the resistance by sacrificing force at the resistance. Different lever styles have different purposes and multiply forces in different ways.