ASVAB Mechanical Comprehension Practice Test 555315 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.21
Score	0%	64%

Review

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
	mechanical advantage
	Pascal's law
	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.

2 A = 9 ft., the green box weighs 35 lbs., and the blue box weighs 85 lbs. What does distance B need to be for this lever to balance?

65% Answer Correctly

	0.93 ft.
	3.71 ft.
	3 ft.
	14.82 ft.

Solution

In order for this lever to balance, the torque acting on side A must equal the torque acting on side B. 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

For this problem, the equation becomes:

35 lbs. x 9 ft. = 85 lbs. x d_B

d_B = \( \frac{35 \times 9 ft⋅lb}{85 lbs.} \) = \( \frac{315 ft⋅lb}{85 lbs.} \) = 3.71 ft.

3 The green box weighs 10 lbs. and a 65 lbs. weight is placed 9 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?

57% Answer Correctly

	234 ft.
	58.5 ft.
	175.5 ft.
	117 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_a, our missing value, and plugging in our variables yields:

d_a = \( \frac{R_bd_b}{R_a} \) = \( \frac{65 lbs. \times 9 ft.}{10 lbs.} \) = \( \frac{585 ft⋅lb}{10 lbs.} \) = 58.5 ft.

A fixed pulley has a mechanical advantage of:

68% Answer Correctly

	0
	1
	-1
	2

Solution

A fixed pulley is used to change the direction of a force and does not multiply the force applied. As such, it has a mechanical advantage of one. The benefit of a fixed pulley is that it can allow the force to be applied at a more convenient angle, for example, pulling downward or horizontally to lift an object instead of upward.

A watt is the unit for which of the following?

71% Answer Correctly

	power
	energy
	mechanical advantage
	work

Solution

Power is the rate at which work is done, P = w/t, or work per unit time. The watt (W) is the unit for power and is equal to 1 joule (or newton-meter) per second. Horsepower (hp) is another familiar unit of power used primarily for rating internal combustion engines. 1 hp equals 746 watts.