ASVAB Mechanical Comprehension Practice Test 584759 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.69
Score	0%	54%

Review

Which of the following will increase the mechanical advantage of a second-class lever?

55% Answer Correctly

	move the fulcrum between the force and the object being lifted
	move the object being lifted farther away from the fulcrum
	decrease the length of the lever
	move the object being lifted closer to the fulcrum

Solution

A second-class lever is used to increase force on an object in the same direction as the force is applied. This lever requires a smaller force to lift a larger load but the force must be applied over a greater distance. The fulcrum is placed at one end of the lever and mechanical advantage increases as the object being lifted is moved closer to the fulcrum or the length of the lever is increased. An example of a second-class lever is a wheelbarrow.

2 If 70 lbs. of force is applied 7 ft. from the fulcrum at the blue arrow and the green box is 5 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?

62% Answer Correctly

	32.67 lbs.
	490 lbs.
	196 lbs.
	98 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 = \( \frac{R_bd_b}{d_a} \) = \( \frac{70 lbs. \times 7 ft.}{5 ft.} \) = \( \frac{490 ft⋅lb}{5 ft.} \) = 98 lbs.

3 A 400 lb. barrel is rolled up a 14 ft. ramp to a platform that's 2 ft. tall. What effort is required to move the barrel?

53% Answer Correctly

	57.1 lbs.
	52.1 lbs.
	19 lbs.
	66.1 lbs.

Solution

This problem describes an inclined plane and, for an inclined plane, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance:

F_ed_e = F_rd_r

Plugging in the variables from this problem yields:

F_e x 14 ft. = 400 lbs. x 2 ft.
F_e = \( \frac{800 ft⋅lb}{14 ft.} \) = 57.1 lbs.

The mechanical advantage of a third class lever is always:

37% Answer Correctly

	equal to one
	not 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.

Two gears are connected and the larger gear drives the smaller gear. The speed of rotation will __________ and the torque will __________.

61% Answer Correctly

	decrease, decrease
	increase, decrease
	increase, increase
	decrease, increase

Solution

Connected gears of different numbers of teeth are used together to change the rotational speed and torque of the input force. If the smaller gear drives the larger gear, the speed of rotation will be reduced and the torque will increase. If the larger gear drives the smaller gear, the speed of rotation will increase and the torque will be reduced.