ASVAB Mechanical Comprehension Practice Test 486269 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.75
Score	0%	55%

Review

1 If the handles of a wheelbarrow are 1.5 ft. from the wheel axle and the load is concentrated at a point 1.5 ft. from the axle, how many pounds of load will a 170 lbs. force lift?

47% Answer Correctly

	170
	0
	75.6
	3.3

Solution

This problem describes a second-class lever and, for a second class lever, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance: F_ed_e = F_rd_r. In this problem we're looking for resistance force:
\( F_r = \frac{F_e d_e}{d_r} \)
\( F_r = \frac{170 \times 1.5}{1.5} \)
\( F_r = \frac{255.0}{1.5} \)
\( F_r = 170 \)

For any given surface, the coefficient of static friction is ___________ the coefficient of kinetic friction.

54% Answer Correctly

	equal to
	opposite
	higher than
	lower than

Solution

For any given surface, the coefficient of static friction is higher than the coefficient of kinetic friction. More force is required to initally get an object moving than is required to keep it moving. Additionally, static friction only arises in response to an attempt to move an object (overcome the normal force between it and the surface).

3 What is the power output of a 3 hp engine that's 55% efficient?

40% Answer Correctly

	18 \( \frac{ft⋅lb}{s} \)
	907.5 \( \frac{ft⋅lb}{s} \)
	302.5 \( \frac{ft⋅lb}{s} \)
	226.9 \( \frac{ft⋅lb}{s} \)

Solution

\( Efficiency = \frac{Power_{out}}{Power_{in}} \times 100 \)
Solving for power out: \( P_{o} = \frac{E \times P_{i}}{100} \)
Knowing that 1 hp = 550 \( \frac{ft⋅lb}{s} \), P_i becomes 3 hp x 550 \( \frac{ft⋅lb}{s} \) = 1650 \( \frac{ft⋅lb}{s} \)
\( P_{o} = \frac{E \times P_{i}}{100} = \frac{55 \times 1650 \frac{ft⋅lb}{s}}{100} \) \( = \frac{90750 \frac{ft⋅lb}{s}}{100} \) = 907.5 \( \frac{ft⋅lb}{s} \)

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

61% Answer Correctly

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

The mass of an object correlates to the size of the object but ultimately depends on:

67% Answer Correctly

	gravity
	the object's weight
	the object's potential energy
	the object's density

Solution

Mass is a measure of the amount of matter in an object. In general, larger objects have larger mass than smaller objects but mass ultimately depends on how compact (dense) a substance is.