ASVAB Mechanical Comprehension Practice Test 451489 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.08
Score	0%	62%

Review

1 If A = 10 ft., B = 1 ft., C = 8 ft., the green box weighs 40 lbs. and the blue box weighs 60 lbs., what does the orange box have to weigh for this lever to balance?

43% Answer Correctly

	10.63 lbs.
	170 lbs.
	42.5 lbs.
	4 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:

40 lbs. x 10 ft. = 60 lbs. x 1 ft. + f_C x 8 ft.

400 ft. lbs. = 60 ft. lbs. + f_C x 8 ft.

f_C = \( \frac{400 ft. lbs. - 60 ft. lbs.}{8 ft.} \) = \( \frac{340 ft. lbs.}{8 ft.} \) = 42.5 lbs.

2 50 lbs. of effort is used by a machine to lift a 400 lbs. box. What is the mechanical advantage of the machine?

84% Answer Correctly

	9.5
	7.2
	24
	8

Solution

Mechanical advantage is resistance force divided by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{400 lbs.}{50 lbs.} \) = 8

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

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

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.

Connected gears of different numbers of teeth are used together to change which of the following charasteristics of the input force?

65% Answer Correctly

	energy
	rotational direction
	force
	torque

Solution

Connected gears of different numbers of teeth are used together to change the rotational speed and torque of the input force. If the smaller gear drives the larger gear, the speed of rotation will be reduced and the torque will increase. If the larger gear drives the smaller gear, the speed of rotation will increase and the torque will be reduced.

Torque involves a perpendicular force applied to a lever arm that moves around a center of rotation. Increasing the length of the lever arm will do which of the following?

54% Answer Correctly

	increase applied force
	increase torque
	decrease applied force
	decrease torque

Solution

Torque measures force applied during rotation: τ = rF. Torque (τ, the Greek letter tau) = the radius of the lever arm (r) multiplied by the force (F) applied. Radius is measured from the center of rotation or fulcrum to the point at which the perpendicular force is being applied. The resulting unit for torque is newton-meter (N-m) or foot-pound (ft-lb).