ASVAB Mechanical Comprehension Practice Test 733014 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.33
Score	0%	67%

Review

The mechanical advantage of a block and tackle is equal to which of the following?

69% Answer Correctly

	the number of input forces
	the number of loads
	the number of connecting ropes
	the number of pulleys

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.

2 If the green arrow in this diagram represents 650 ft⋅lb of work, how far will the box move if it weighs 130 pounds?

73% Answer Correctly

	20 ft.
	26 ft.
	65 ft.
	5 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 650 ft⋅lb and the resistance force is 130 lbs. and we need to calculate the resistance distance:

W_in = F_resistance x d_resistance
650 ft⋅lb = 130 lbs. x d_resistance
d_resistance = \( \frac{650ft⋅lb}{130 lbs.} \) = 5 ft.

A a seesaw / teeter-totter is an example of which of the following?

69% Answer Correctly

	first-class lever
	third-class lever
	inclined plane
	second-class lever

Solution

A first-class lever is used to increase force or distance while changing the direction of the force. The lever pivots on a fulcrum and, when a force is applied to the lever at one side of the fulcrum, the other end moves in the opposite direction. The position of the fulcrum also defines the mechanical advantage of the lever. If the fulcrum is closer to the force being applied, the load can be moved a greater distance at the expense of requiring a greater input force. If the fulcrum is closer to the load, less force is required but the force must be applied over a longer distance. An example of a first-class lever is a seesaw / teeter-totter.

4 If the green box weighs 20 lbs. and 50 lbs. of force is applied 7 ft. from the fulcrum at the blue arrow, how far from the fulcrum would the green box need to be placed to balance the lever?

55% Answer Correctly

	17.5 ft.
	35 ft.
	70 ft.
	8.75 ft.

Solution

To balance this lever the torques at the green box and the blue arrow 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 green box and b the blue arrow, R is resistance (weight/force) and d is the distance from the fulcrum.

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

d_a = \( \frac{R_bd_b}{R_a} \) = \( \frac{50 lbs. \times 7 ft.}{20 lbs.} \) = \( \frac{350 ft⋅lb}{20 lbs.} \) = 17.5 ft.

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

66% Answer Correctly

	concentrated load
	static load
	dynamic load
	impact 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.