ASVAB Mechanical Comprehension Practice Test 977847 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.03
Score	0%	61%

Review

Which of the following represents the force a surface exerts when an object presses against it?

48% Answer Correctly

	mass
	friction
	normal force
	counter force

Solution

Normal force (F_N) represents the force a surface exerts when an object presses against it.

2 If the green arrow in this diagram represents 560 ft⋅lb of work, how far will the box move if it weighs 140 pounds?

72% Answer Correctly

	4 ft.
	560 ft.
	35 ft.
	16 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 560 ft⋅lb and the resistance force is 140 lbs. and we need to calculate the resistance distance:

W_in = F_resistance x d_resistance
560 ft⋅lb = 140 lbs. x d_resistance
d_resistance = \( \frac{560ft⋅lb}{140 lbs.} \) = 4 ft.

3 If the green box weighs 75 lbs. and is 9 ft. from the fulcrum, how far from the fulcrum would a 45 lbs. weight need to be placed to balance the lever?

61% Answer Correctly

	15 ft.
	675 ft.
	30 ft.
	0 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 = \( \frac{R_ad_a}{R_b} \) = \( \frac{75 lbs. \times 9 ft.}{45 lbs.} \) = \( \frac{675 ft⋅lb}{45 lbs.} \) = 15 ft.

Two or more pulleys used together are called:

71% Answer Correctly

	gears
	block and tackle
	wheel and axle
	third-class lever

Solution

Two or more pulleys used together constitute a block and tackle which, unlike a fixed pulley, does impart mechanical advantage as a function of the number of pulleys that make up the arrangement. So, for example, a block and tackle with three pulleys would have a mechanical advantage of three.

5 The radius of the axle is 5, the radius of the wheel is 8, and the blue box weighs 25 lbs. What is the effort force necessary to balance the load?

53% Answer Correctly

	9.6 lbs.
	13 lbs.
	15.63 lbs.
	40 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 8 and the output radius (where the resistance is being applied) is 5 for a mechanical advantage of \( \frac{8}{5} \) = 1.6

MA = \( \frac{load}{effort} \) so effort = \( \frac{load}{MA} \) = \( \frac{25 lbs.}{1.6} \) = 15.63 lbs.