ASVAB Mechanical Comprehension Practice Test 112751 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.84
Score	0%	57%

Review

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

38% Answer Correctly

	idler gear
	output gear
	driven gear
	driver 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.

When all forces acting on a system cancel each other out, this is called:

80% Answer Correctly

	equilibrium
	stasis
	rest
	potential energy

Solution

When a system is stable or balanced (equilibrium) all forces acting on the system cancel each other out. In the case of torque, equilibrium means that the sum of the anticlockwise moments about a center of rotation equal the sum of the clockwise moments.

3 If the green arrow in this diagram represents 390 ft⋅lb of work, how far will the box move if it weighs 130 pounds?

72% Answer Correctly

	3 ft.
	43 ft.
	12 ft.
	65 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 390 ft⋅lb and the resistance force is 130 lbs. and we need to calculate the resistance distance:

W_in = F_resistance x d_resistance
390 ft⋅lb = 130 lbs. x d_resistance
d_resistance = \( \frac{390ft⋅lb}{130 lbs.} \) = 3 ft.

4 The radius of the axle is 5, the radius of the wheel is 10, and the blue box weighs 55 lbs. What is the effort force necessary to balance the load?

53% Answer Correctly

	27.5 lbs.
	50 lbs.
	5 lbs.
	15 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 10 and the output radius (where the resistance is being applied) is 5 for a mechanical advantage of \( \frac{10}{5} \) = 2.0

MA = \( \frac{load}{effort} \) so effort = \( \frac{load}{MA} \) = \( \frac{55 lbs.}{2.0} \) = 27.5 lbs.

5 If A = 10 ft., B = 2 ft., C = 7 ft., the green box weighs 45 lbs. and the blue box weighs 60 lbs., what does the orange box have to weigh for this lever to balance?

43% Answer Correctly

	11.79 lbs.
	94.29 lbs.
	47.14 lbs.
	15.71 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:

45 lbs. x 10 ft. = 60 lbs. x 2 ft. + f_C x 7 ft.

450 ft. lbs. = 120 ft. lbs. + f_C x 7 ft.

f_C = \( \frac{450 ft. lbs. - 120 ft. lbs.}{7 ft.} \) = \( \frac{330 ft. lbs.}{7 ft.} \) = 47.14 lbs.