ASVAB Mechanical Comprehension Practice Test 815597 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.22
Score	0%	64%

Review

Friction resists movement in a direction __________ to the movement.

82% Answer Correctly

	opposite
	normal
	parallel
	perpendicular

Solution

Friction resists movement. Kinetic (also called sliding or dynamic) friction resists movement in a direction opposite to the movement. Because it opposes movement, kinetic friction will eventually bring an object to a stop. An example is a rock that's sliding across ice.

2 If A = 12 ft., B = 1 ft., C = 7 ft., the green box weighs 30 lbs. and the blue box weighs 50 lbs., what does the orange box have to weigh for this lever to balance?

44% Answer Correctly

	177.14 lbs.
	30 lbs.
	44.29 lbs.
	11.07 lbs.

Solution

In order for this lever to balance, the torque acting on each side of the fulrum must be equal. So, the torque produced by A must equal the torque produced by B and C. Torque is weight x distance from the fulcrum which means that the following must be true for the lever to balance:

f_Ad_A = f_Bd_B + f_Cd_C

For this problem, this equation becomes:

30 lbs. x 12 ft. = 50 lbs. x 1 ft. + f_C x 7 ft.

360 ft. lbs. = 50 ft. lbs. + f_C x 7 ft.

f_C = \( \frac{360 ft. lbs. - 50 ft. lbs.}{7 ft.} \) = \( \frac{310 ft. lbs.}{7 ft.} \) = 44.29 lbs.

3 If the green box weighs 70 lbs. and 5 lbs. of force is applied 5 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

	0.36 ft.
	0 ft.
	350 ft.
	14 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 = \( \frac{R_bd_b}{R_a} \) = \( \frac{5 lbs. \times 5 ft.}{70 lbs.} \) = \( \frac{25 ft⋅lb}{70 lbs.} \) = 0.36 ft.

The work done by the sum of all forces acting on a particle equals the change in the kinetic energy of the particle. This defines which of the following?

60% Answer Correctly

	conservation of mechanical energy
	Pascal's law
	work-energy theorem
	mechanical advantage

Solution

The work-energy theorem states that the work done by the sum of all forces acting on a particle equals the change in the kinetic energy of the particle. Simply put, work imparts kinetic energy to the matter upon which the work is being done.

The mechanical advantage of connected gears is proportional to which characteristic of the gears?

73% Answer Correctly

	number of teeth
	circumference
	speed
	diameter

Solution

The mechanical advantage (amount of change in speed or torque) of connected gears is proportional to the number of teeth each gear has. Called gear ratio, it's the ratio of the number of teeth on the larger gear to the number of teeth on the smaller gear. For example, a gear with 12 teeth connected to a gear with 9 teeth would have a gear ratio of 4:3.