ASVAB Mechanical Comprehension Practice Test 474576 Results

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

Review

1

A box is resting on a smooth floor. Static friction is present:

59% Answer Correctly

at all times

if the coefficient of friction is greater than one

only if normal force is present

when an attempt is made to move the box
Solution

For any given surface, the coefficient of static friction is higher than the coefficient of kinetic friction. More force is required to initally get an object moving than is required to keep it moving. Additionally, static friction only arises in response to an attempt to move an object (overcome the normal force between it and the surface).

2 If A = 3 ft. and the green box weighs 45 lbs. what is the torque acting on the A side of this lever?
74% Answer Correctly
15 ft⋅lb
540 ft⋅lb
135 ft⋅lb
33 ft⋅lb
Solution
For a lever, torque is weight x distance from the fulcrum which, in this case, is: 45 ft. x 3 lbs. = 135 ft⋅lb
3 If the green box weighs 45 lbs. and is 7 ft. from the fulcrum, how far from the fulcrum would a 55 lbs. force need to be applied to balance the lever?
58% Answer Correctly
0 ft.
5.73 ft.
17.18 ft.
11.45 ft.
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 db, our missing value, and plugging in our variables yields:

db = \( \frac{R_ad_a}{R_b} \) = \( \frac{45 lbs. \times 7 ft.}{55 lbs.} \) = \( \frac{315 ft⋅lb}{55 lbs.} \) = 5.73 ft.

4

A fixed pulley has a mechanical advantage of:

68% Answer Correctly

-1

1

2

0
Solution

A fixed pulley is used to change the direction of a force and does not multiply the force applied. As such, it has a mechanical advantage of one. The benefit of a fixed pulley is that it can allow the force to be applied at a more convenient angle, for example, pulling downward or horizontally to lift an object instead of upward.

5 A 350 lb. barrel is rolled up a 12 ft. ramp to a platform that's 2 ft. tall. What effort is required to move the barrel?
53% Answer Correctly
52.5 lbs.
60.3 lbs.
58.3 lbs.
116.7 lbs.
Solution

This problem describes an inclined plane and, for an inclined plane, 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 12 ft. = 350 lbs. x 2 ft.
Fe = \( \frac{700 ft⋅lb}{12 ft.} \) = 58.3 lbs.