ASVAB Mechanical Comprehension Practice Test 21980 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.66
Score	0%	53%

Review

1 If the handles of a wheelbarrow are 2.0 ft. from the wheel axle, how many pounds of force must you exert to lift the handles if it's carrying a 110 lbs. load concentrated at a point 1.0 ft. from the axle?

52% Answer Correctly

	55
	52.5
	110
	None of these is correct

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 effort force:
\( F_e = \frac{F_r d_r}{d_e} \)
\( F_e = \frac{110 \times 1.0}{2.0} \)
\( F_e = \frac{110.0}{2.0} \)
\( F_e = 55 \)

A fixed pulley is useful for which of the following?

53% Answer Correctly

	multiplying the input force
	changing the direction of the output force
	changing the direction of the input force
	multiplying the input distance

Solution

A fixed pulley is used to change the direction of a force and does not multiply the force applied. As such, it has a mechanical advantage of one. The benefit of a fixed pulley is that it can allow the force to be applied at a more convenient angle, for example, pulling downward or horizontally to lift an object instead of upward.

Power is the rate at which:

62% Answer Correctly

	friction is overcome
	input force is transferred to output force
	potential energy is converted into kinetic energy
	work is done

Solution

Power is the rate at which work is done, P = w/t, or work per unit time. The watt (W) is the unit for power and is equal to 1 joule (or newton-meter) per second. Horsepower (hp) is another familiar unit of power used primarily for rating internal combustion engines. 1 hp equals 746 watts.

Normal force is generally equal to the __________ of an object.

61% Answer Correctly

	coefficient of friction
	mass
	weight
	density

Solution

Normal force arises on a flat horizontal surface in response to an object's weight pressing it down. Consequently, normal force is generally equal to the object's weight.

The mechanical advantage of a third class lever is always:

37% Answer Correctly

	not equal to one
	equal to one
	less than one
	greater than one

Solution

A third class lever is designed to multiply distance and speed at the expense of effort force. Because the effort force is greater than the resistance, the mechanical advantage of a third class lever is always less than one.

An example of a third class lever is a broom. The fulcrum is at your hand on the end of the broom, the effort force is your other hand in the middle, and the resistance is at the bottom bristles. The effort force of your hand in the middle multiplies the distance and speed of the bristles at the bottom but at the expense of producing a brushing force that's less than the force you're applying with your hand.