ASVAB Mechanical Comprehension Practice Test 884871 Results

Your Results Global Average
Questions 5 5
Correct 0 3.01
Score 0% 60%

Review

1 If the green box weighs 45 lbs. and is 5 ft. from the fulcrum, how much force would need to be applied at the blue arrow to balance the lever if the arrow's distance from the fulcrum is 9 ft.?
62% Answer Correctly
75 lbs.
25 lbs.
50 lbs.
405 lbs.
Solution

To balance this lever the torques at the green box and the blue arrow must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:

Rada = Rbdb

where a represents the green box and b the blue arrow, R is resistance (weight/force) and d is the distance from the fulcrum.

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

Rb = \( \frac{R_ad_a}{d_b} \) = \( \frac{45 lbs. \times 5 ft.}{9 ft.} \) = \( \frac{225 ft⋅lb}{9 ft.} \) = 25 lbs.

2

If the handles of a wheelbarrow are 3 ft. from the wheel axle, what force must you exert to lift the handles if it's carrying a 270 lb. load concentrated at a point 0.5 ft. from the axle?

56% Answer Correctly

0.83 lbs

45 lbs

810 lbs

90 lbs
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. Plugging in the variables from this problem yields:

Fe x 3 ft. = 270 lbs x 0.5 ft
Fe = 135 ft-lb. / 3 ft 
Fe = 45 lbs

3

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

85% Answer Correctly

none of these

first-class lever

wedge

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

The principle of conservation of mechanical energy states that, as long as no other forces are applied, what will remain constant as an object falls?

45% Answer Correctly

total mechanical energy

kinetic energy

acceleration

potential energy
Solution

As an object falls, its potential energy is converted into kinetic energy. The principle of conservation of mechanical energy states that, as long as no other forces are applied, total mechanical energy (PE + KE) of the object will remain constant at all points in its descent.

5 If the handles of a wheelbarrow are 1.5 ft. from the wheel axle, how many pounds of force must you exert to lift the handles if it's carrying a 180 lbs. load concentrated at a point 1.0 ft. from the axle?
52% Answer Correctly
None of these is correct
120
398
52.3
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 effort force:
\( F_e = \frac{F_r d_r}{d_e} \)
\( F_e = \frac{180 \times 1.0}{1.5} \)
\( F_e = \frac{180.0}{1.5} \)
\( F_e = 120 \)