ASVAB Mechanical Comprehension Practice Test 85893 Results

Your Results Global Average
Questions 5 5
Correct 0 3.26
Score 0% 65%

Review

1

A fixed pulley has a mechanical advantage of:

68% Answer Correctly

0

1

-1

2
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.

2 If the green box weighs 45 lbs. and 65 lbs. of force is applied 5 ft. from the fulcrum at the blue arrow, how far from the fulcrum would the green box need to be placed to balance the lever?
55% Answer Correctly
3.61 ft.
7.22 ft.
28.89 ft.
21.67 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 da, our missing value, and plugging in our variables yields:

da = \( \frac{R_bd_b}{R_a} \) = \( \frac{65 lbs. \times 5 ft.}{45 lbs.} \) = \( \frac{325 ft⋅lb}{45 lbs.} \) = 7.22 ft.

3 If the green box weighs 65 lbs. and is 3 ft. from the fulcrum, how much weight would need to be placed at the blue arrow to balance the lever if the arrow's distance from the fulcrum is 2 ft.?
63% Answer Correctly
48.75 lbs.
97.5 lbs.
24.38 lbs.
195 lbs.
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 Rb, our missing value, and plugging in our variables yields:

Rb = \( \frac{R_ad_a}{d_b} \) = \( \frac{65 lbs. \times 3 ft.}{2 ft.} \) = \( \frac{195 ft⋅lb}{2 ft.} \) = 97.5 lbs.

4

Power is the rate at which:

62% Answer Correctly

work is done

input force is transferred to output force

potential energy is converted into kinetic energy

friction is overcome
Solution

Power is the rate at which work is done, P = w/t, or work per unit time. The watt (W) is the unit for power and is equal to 1 joule (or newton-meter) per second. Horsepower (hp) is another familiar unit of power used primarily for rating internal combustion engines. 1 hp equals 746 watts.

5 If input effort is 100 ft⋅lb, what output effort will be produced by a machine with a mechanical advantage of 7?
79% Answer Correctly
14ft⋅lb
175ft⋅lb
1400ft⋅lb
700 ft⋅lb
Solution
Mechanical advantage is the ratio of output force to input force and tells us by how many times a machine multiplies input effort. So, a machine with a mechanical advantage of 7 will multiply an input effort of 100 ft⋅lb by 7 to produce an output effort of 700 ft⋅lb.