ASVAB Mechanical Comprehension Practice Test 90505 Results

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

Review

1 If the force applied at the blue arrow over 4 ft. moves the green box 0.67 ft., what is the mechanical advantage of this lever?

56% Answer Correctly

	2
	3
	6
	5.4

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 = \( \frac{4 ft.}{0.67 ft.} \) = 6

You might be wondering how having an effort distance of 6 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 6 times the resistance distance, the effort force must be \( \frac{1}{6} \) the resistance force. You're trading moving 6 times the distance for only having to use \( \frac{1}{6} \) the force.

2 If the green box weighs 35 lbs. and is 1 ft. from the fulcrum, how far from the fulcrum would a 50 lbs. weight need to be placed to balance the lever?

61% Answer Correctly

	1.4 ft.
	0.18 ft.
	0.7 ft.
	2.1 ft.

Solution

To balance this lever the torques on each side of the fulcrum must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:

R_ad_a = R_bd_b

where a represents the left side of the fulcrum and b the right, R is resistance (weight) and d is the distance from the fulcrum.

Solving for d_b, our missing value, and plugging in our variables yields:

d_b = \( \frac{R_ad_a}{R_b} \) = \( \frac{35 lbs. \times 1 ft.}{50 lbs.} \) = \( \frac{35 ft⋅lb}{50 lbs.} \) = 0.7 ft.

3 If the radius of the axle is 5 and the radius of the wheel is 6, what is the mechanical advantage of this wheel and axle configuration?

36% Answer Correctly

	1
	6
	1
	5

Solution

The mechanical advantage of a wheel and axle lies in the difference in radius between the inner (axle) wheel and the outer wheel. But, this mechanical advantage is only realized when the input effort and load are applied to different wheels. Applying both input effort and load to the same wheel results in a mechanical advantage of 1.

What type of load varies with time or affects a structure that experiences a high degree of movement?

65% Answer Correctly

	dynamic load
	impact load
	static load
	concentrated load

Solution

A concentrated load acts on a relatively small area of a structure, a static uniformly distributed load doesn't create specific stress points or vary with time, a dynamic load varies with time or affects a structure that experiences a high degree of movement, an impact load is sudden and for a relatively short duration and a non-uniformly distributed load creates different stresses at different locations on a structure.

A block and tackle with four pulleys would have a mechanical advantage of:

79% Answer Correctly

	1
	2
	4
	0

Solution

Two or more pulleys used together constitute a block and tackle which, unlike a fixed pulley, does impart mechanical advantage as a function of the number of pulleys that make up the arrangement. So, for example, a block and tackle with three pulleys would have a mechanical advantage of three.