ASVAB Mechanical Comprehension Practice Test 783677 Results

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

Review

1

Which of the following is the formula for gravitational potential energy?

61% Answer Correctly

\(PE = { 1 \over 2} mg^2\)

\(PE = mg^2h\)

\(PE = { 1 \over 2} mv^2\)

\(PE = mgh\)
Solution

Gravitational potential energy is energy by virtue of gravity. The higher an object is raised above a surface the greater the distance it must fall to reach that surface and the more velocity it will build as it falls. For gravitational potential energy, PE = mgh where m is mass (kilograms), h is height (meters), and g is acceleration due to gravity which is a constant (9.8 m/s2).

2

The mechanical advantage of a block and tackle is equal to which of the following?

69% Answer Correctly

the number of pulleys

the number of loads

the number of input forces

the number of connecting ropes
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.

3

A ramp is an example of which kind of simple machine?

84% Answer Correctly

wedge

first-class lever

none of these

inclined plane
Solution

An inclined plane is a simple machine that reduces the force needed to raise an object to a certain height. Work equals force x distance and, by increasing the distance that the object travels, an inclined plane reduces the force necessary to raise it to a particular height. In this case, the mechanical advantage is to make the task easier. An example of an inclined plane is a ramp.

4

Gear ratio indicates which of the following about two connected gears?

59% Answer Correctly

mechanical advantage

work done

power conversion

efficiency
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.

5 What is the power output of a 7 hp engine that's 65% efficient?
40% Answer Correctly
2502.5 \( \frac{ft⋅lb}{s} \)
625.6 \( \frac{ft⋅lb}{s} \)
0 \( \frac{ft⋅lb}{s} \)
834.2 \( \frac{ft⋅lb}{s} \)
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 \( \frac{ft⋅lb}{s} \), Pi becomes 7 hp x 550 \( \frac{ft⋅lb}{s} \) = 3850 \( \frac{ft⋅lb}{s} \)
\( P_{o} = \frac{E \times P_{i}}{100} = \frac{65 \times 3850 \frac{ft⋅lb}{s}}{100} \) \( = \frac{250250 \frac{ft⋅lb}{s}}{100} \) = 2502.5 \( \frac{ft⋅lb}{s} \)