ASVAB Mechanical Comprehension Practice Test 55770 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.83
Score	0%	57%

Review

Two gears are connected and the larger gear drives the smaller gear. The speed of rotation will __________ and the torque will __________.

61% Answer Correctly

	increase, increase
	increase, decrease
	decrease, decrease
	decrease, increase

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.

2 If the green arrow in this diagram represents 920 ft⋅lb of work, how far will the box move if it weighs 230 pounds?

72% Answer Correctly

	8 ft.
	16 ft.
	57 ft.
	4 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 920 ft⋅lb and the resistance force is 230 lbs. and we need to calculate the resistance distance:

W_in = F_resistance x d_resistance
920 ft⋅lb = 230 lbs. x d_resistance
d_resistance = \( \frac{920ft⋅lb}{230 lbs.} \) = 4 ft.

Depending on where you apply effort and resistance, the wheel and axle can multiply:

45% Answer Correctly

	power or distance
	force or distance
	speed or power
	force or speed

Solution

If you apply the resistance to the axle and the effort to the wheel, the wheel and axle will multiply force and if you apply the resistance to the wheel and the effort to the axle, it will multiply speed.

The principle of conservation of mechanical energy states that, as long as no other forces are applied, what will remain constant as an object falls?

45% Answer Correctly

	acceleration
	potential energy
	kinetic energy
	total mechanical energy

Solution

As an object falls, its potential energy is converted into kinetic energy. The principle of conservation of mechanical energy states that, as long as no other forces are applied, total mechanical energy (PE + KE) of the object will remain constant at all points in its descent.

5 If the green box weighs 35 lbs. and is 7 ft. from the fulcrum, how far from the fulcrum would a 70 lbs. weight need to be placed to balance the lever?

60% Answer Correctly

	0 ft.
	3.5 ft.
	7 ft.
	14 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_b, our missing value, and plugging in our variables yields:

d_b = \( \frac{R_ad_a}{R_b} \) = \( \frac{35 lbs. \times 7 ft.}{70 lbs.} \) = \( \frac{245 ft⋅lb}{70 lbs.} \) = 3.5 ft.