ASVAB Mechanical Comprehension Practice Test 233568 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.14
Score	0%	63%

Review

1 What is the efficiency of a machine has work input of 110 ft⋅lb and work output of 44 ft⋅lb?

67% Answer Correctly

	80%
	20%
	40%
	2%

Solution

Due to friction, a machine will never be able to utilize 100% of its work input. A certain percentage of that input will be lost in overcoming friction within the machine. Effeciency is a measure of how much of a machine's work input can be turned into useful work output and is calculated by dividing work output by work input and multiplying the result by 100:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{44 ft⋅lb}{110 ft⋅lb} \times 100 \) \( = 40% \) %

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

61% Answer Correctly

	increase, decrease
	decrease, increase
	increase, increase
	decrease, 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.

Potential energy is energy that has the potential to be converted into what?

80% Answer Correctly

	power
	kinetic energy
	work
	heat

Solution

Potential energy is the energy of an object by virtue of its position relative to other objects. It is energy that has the potential to be converted into kinetic energy.

Which of the following is not a modulus of elasticity?

47% Answer Correctly

	bulk modulus
	stretch modulus
	shear modulus
	stress modulus

Solution

The modulus of elasticity measures how much a material or structure will deflect under stress. Stretch modulus is longitudinal stretch (like stretching raw bread dough), shear modulus is longitudinal deflection (like the horizontal displacement of a stack of magzines when a heavy object is placed upon them), and bulk modulus is compression of volume (like the compression of a loaf of bread under a heavy can at the bottom of a grocery bag).

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

59% Answer Correctly

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

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).