ASVAB Mechanical Comprehension Practice Test 903089 Results

Your Results Global Average
Questions 5 5
Correct 0 3.43
Score 0% 69%

Review

1

The mechanical advantage of connected gears is proportional to which characteristic of the gears?

73% Answer Correctly

number of teeth

circumference

diameter

speed
Solution

The mechanical advantage (amount of change in speed or torque) of connected gears is proportional to the number of teeth each gear has. Called gear ratio, it's the ratio of the number of teeth on the larger gear to the number of teeth on the smaller gear.  For example, a gear with 12 teeth connected to a gear with 9 teeth would have a gear ratio of 4:3.

2

Friction resists movement in a direction __________ to the movement.

81% Answer Correctly

opposite

normal

perpendicular

parallel
Solution

Friction resists movement. Kinetic (also called sliding or dynamic) friction resists movement in a direction opposite to the movement. Because it opposes movement, kinetic friction will eventually bring an object to a stop. An example is a rock that's sliding across ice.

3 What is the efficiency of a machine has work input of 120 ft⋅lb and work output of 84 ft⋅lb?
67% Answer Correctly
35%
1%
70%
0%
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:
\( Efficiency = \frac{Work_{out}}{Work_{in}} \times 100 \) \( = \frac{84 ft⋅lb}{120 ft⋅lb} \times 100 \) \( = 70% \) %
4

Which of the following is the formula for torque?

61% Answer Correctly

τ = r/F

τ = rF

τ = F/r

τ = F/r2
Solution

Torque measures force applied during rotation: τ = rF.  Torque (τ, the Greek letter tau) = the radius of the lever arm (r) multiplied by the force (F) applied. Radius is measured from the center of rotation or fulcrum to the point at which the perpendicular force is being applied. The resulting unit for torque is newton-meter (N-m) or foot-pound (ft-lb).

5

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.