ASVAB Mechanical Comprehension Practice Test 776151 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.21
Score	0%	64%

Review

A block and tackle with four pulleys would have a mechanical advantage of:

79% Answer Correctly

	4
	1
	2
	0

Solution

Two or more pulleys used together constitute a block and tackle which, unlike a fixed pulley, does impart mechanical advantage as a function of the number of pulleys that make up the arrangement. So, for example, a block and tackle with three pulleys would have a mechanical advantage of three.

2 If you have a gear train with two gears, the first with 40 teeth and the second with 16 teeth, how many revolutions does the second gear make for each revolution of the first gear?

78% Answer Correctly

	2.5
	10.5
	5
	-1.5

Solution

The gear ratio (V_r) of a gear train is the product of the gear ratios between the pairs of meshed gears. Let N represent the number of teeth for each gear:

V_r = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) \( \frac{N_3}{N_4} \) ... \( \frac{N_n}{N_{n+1}} \)

In this problem, we have only two gears so the equation becomes:

V_r = \( \frac{N_1}{N_2} \) = \( \frac{40}{16} \) = 2.5

3 What is the power output of a 4 hp engine that's 30% efficient?

40% Answer Correctly

	7 \( \frac{ft⋅lb}{s} \)
	330 \( \frac{ft⋅lb}{s} \)
	660 \( \frac{ft⋅lb}{s} \)
	0 \( \frac{ft⋅lb}{s} \)

Solution

\( Efficiency = \frac{Power_{out}}{Power_{in}} \times 100 \)
Solving for power out: \( P_{o} = \frac{E \times P_{i}}{100} \)
Knowing that 1 hp = 550 \( \frac{ft⋅lb}{s} \), P_i becomes 4 hp x 550 \( \frac{ft⋅lb}{s} \) = 2200 \( \frac{ft⋅lb}{s} \)
\( P_{o} = \frac{E \times P_{i}}{100} = \frac{30 \times 2200 \frac{ft⋅lb}{s}}{100} \) \( = \frac{66000 \frac{ft⋅lb}{s}}{100} \) = 660 \( \frac{ft⋅lb}{s} \)

According to Boyle's law, for a fixed amount of gas kept at a fixed temperature, which of the following are inversely proportional?

63% Answer Correctly

	density, volume
	volume, mass
	pressure, density
	pressure, volume

Solution

Boyle's law states that "for a fixed amount of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional".

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.