ASVAB Mechanical Comprehension Practice Test 481698 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.04
Score	0%	61%

Review

The mechanical advantage of a wheel and axle is equal to the:

61% Answer Correctly

	length of the axle
	difference in the lengths of the axles
	difference in the diameters of the wheels
	ratio of the diameters of the wheels

Solution

A wheel and axle uses two different diameter wheels mounted to a connecting axle. Force is applied to the larger wheel and large movements of this wheel result in small movements in the smaller wheel. Because a larger movement distance is being translated to a smaller distance, force is increased with a mechanical advantage equal to the ratio of the diameters of the wheels. An example of a wheel and axle is the steering wheel of a car.

Which of the following is the formula for gravitational potential energy?

61% Answer Correctly

	\(PE = { 1 \over 2} mv^2\)
	\(PE = mg^2h\)
	\(PE = mgh\)
	\(PE = { 1 \over 2} mg^2\)

Solution

Gravitational potential energy is energy by virtue of gravity. The higher an object is raised above a surface the greater the distance it must fall to reach that surface and the more velocity it will build as it falls. For gravitational potential energy, PE = mgh where m is mass (kilograms), h is height (meters), and g is acceleration due to gravity which is a constant (9.8 m/s²).

Friction resists movement in a direction __________ to the movement.

81% Answer Correctly

	opposite
	normal
	parallel
	perpendicular

Solution

Friction resists movement. Kinetic (also called sliding or dynamic) friction resists movement in a direction opposite to the movement. Because it opposes movement, kinetic friction will eventually bring an object to a stop. An example is a rock that's sliding across ice.

4 If A = 10 ft., B = 2 ft., C = 5 ft., the green box weighs 35 lbs. and the blue box weighs 40 lbs., what does the orange box have to weigh for this lever to balance?

44% Answer Correctly

	162 lbs.
	54 lbs.
	13.5 lbs.
	216 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 10 ft. = 40 lbs. x 2 ft. + f_C x 5 ft.

350 ft. lbs. = 80 ft. lbs. + f_C x 5 ft.

f_C = \( \frac{350 ft. lbs. - 80 ft. lbs.}{5 ft.} \) = \( \frac{270 ft. lbs.}{5 ft.} \) = 54 lbs.

5 If the radius of the axle is 5 and the radius of the wheel is 10, what is the mechanical advantage of this wheel and axle configuration?

52% Answer Correctly

	2.0
	5
	-5
	10

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 10 and the output radius (where the resistance is being applied) is 5 for a mechanical advantage of \( \frac{10}{5} \) = 2.0