ASVAB Mechanical Comprehension Practice Test 609146 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.07
Score	0%	61%

Review

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

45% Answer Correctly

	speed or power
	power or distance
	force or distance
	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.

2 If A = 9 ft., B = 3 ft., C = 8 ft., the green box weighs 35 lbs. and the blue box weighs 55 lbs., what does the orange box have to weigh for this lever to balance?

44% Answer Correctly

	105 lbs.
	18.75 lbs.
	0 lbs.
	6.25 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:

35 lbs. x 9 ft. = 55 lbs. x 3 ft. + f_C x 8 ft.

315 ft. lbs. = 165 ft. lbs. + f_C x 8 ft.

f_C = \( \frac{315 ft. lbs. - 165 ft. lbs.}{8 ft.} \) = \( \frac{150 ft. lbs.}{8 ft.} \) = 18.75 lbs.

3 If 15 lbs. of force is applied 8 ft. from the fulcrum at the blue arrow and the green box is 4 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?

62% Answer Correctly

	90 lbs.
	120 lbs.
	30 lbs.
	7.5 lbs.

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 R_a, our missing value, and plugging in our variables yields:

R_a = \( \frac{R_bd_b}{d_a} \) = \( \frac{15 lbs. \times 8 ft.}{4 ft.} \) = \( \frac{120 ft⋅lb}{4 ft.} \) = 30 lbs.

4 What is the mechanical advantage of this inclined plane if the length of the ramp is 5 ft. and the height of the green box is 1 ft.?

82% Answer Correctly

	5
	-1
	15
	1

Solution

The mechanical advantage (MA) of an inclined plane is the effort distance divided by the resistance distance. In this case, the effort distance is the length of the ramp and the resistance distance is the height of the green box:

MA = \( \frac{d_e}{d_r} \) = \( \frac{5 ft.}{1 ft.} \) = 5

5 If the green arrow in this diagram represents 450 ft⋅lb of work, how far will the box move if it weighs 90 pounds?

73% Answer Correctly

	1 ft.
	10 ft.
	5 ft.
	0 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 450 ft⋅lb and the resistance force is 90 lbs. and we need to calculate the resistance distance:

W_in = F_resistance x d_resistance
450 ft⋅lb = 90 lbs. x d_resistance
d_resistance = \( \frac{450ft⋅lb}{90 lbs.} \) = 5 ft.