ASVAB Mechanical Comprehension Practice Test 980837 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.24
Score	0%	65%

Review

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

61% Answer Correctly

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

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.

A box is resting on a smooth floor. Static friction is present:

59% Answer Correctly

	when an attempt is made to move the box
	at all times
	only if normal force is present
	if the coefficient of friction is greater than one

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 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

	560 ft.
	35 ft.
	8 ft.
	4 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.

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

55% Answer Correctly

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

5 If input effort is 800 ft⋅lb, what output effort will be produced by a machine with a mechanical advantage of 8?

79% Answer Correctly

	12800ft⋅lb
	3200ft⋅lb
	6400 ft⋅lb
	0ft⋅lb

Solution

Mechanical advantage is the ratio of output force to input force and tells us by how many times a machine multiplies input effort. So, a machine with a mechanical advantage of 8 will multiply an input effort of 800 ft⋅lb by 8 to produce an output effort of 6400 ft⋅lb.