ASVAB Mechanical Comprehension Practice Test 470517 Results

Your Results Global Average
Questions 5 5
Correct 0 2.89
Score 0% 58%

Review

1 If the green box weighs 65 lbs. and is 9 ft. from the fulcrum, how far from the fulcrum would a 15 lbs. weight need to be placed to balance the lever?
61% Answer Correctly
156 ft.
78 ft.
13 ft.
39 ft.
Solution

To balance this lever the torques on each side of the fulcrum must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:

Rada = Rbdb

where a represents the left side of the fulcrum and b the right, R is resistance (weight) and d is the distance from the fulcrum.

Solving for db, our missing value, and plugging in our variables yields:

db = \( \frac{R_ad_a}{R_b} \) = \( \frac{65 lbs. \times 9 ft.}{15 lbs.} \) = \( \frac{585 ft⋅lb}{15 lbs.} \) = 39 ft.

2

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

61% Answer Correctly

\(PE = mg^2h\)

\(PE = mgh\)

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

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

3

What is the first step to solving a problem where multiple forces are acting on an object?

61% Answer Correctly

calculate the total force

calculate potential energy

calculate the net force

calculate kinetic energy
Solution

In mechanics, multiple forces are often acting on a particular object and, taken together, produce the net force acting on that object. Like force, net force is a vector quantity in that it has magnitude and direction.

4 If the handles of a wheelbarrow are 1.0 ft. from the wheel axle and the load is concentrated at a point 1.5 ft. from the axle, how many pounds of load will a 230 lbs. force lift?
47% Answer Correctly
230
153.3
345
125.6
Solution
This problem describes a second-class lever and, for a second class lever, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance: Fede = Frdr. In this problem we're looking for resistance force:
\( F_r = \frac{F_e d_e}{d_r} \)
\( F_r = \frac{230 \times 1.0}{1.5} \)
\( F_r = \frac{230.0}{1.5} \)
\( F_r = 153.3 \)
5

An inclined plane increases ___________ to reduce ____________.

58% Answer Correctly

distance, power

distance, force

force, power

force, distance
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.