ASVAB Mechanical Comprehension Practice Test 245568 Results

Your Results Global Average
Questions 5 5
Correct 0 3.27
Score 0% 65%

Review

1 If this lever is in equilibrium with an effort force of 20.0 ft. lb. at the blue arrow and a resistance force of 4 ft. lb. at the green box, what is its mechanical advantage?
48% Answer Correctly
0.3
3.2
0.2
-8.8
Solution

Mechanical advantage (MA) is the ratio by which effort force relates to resistance force. If both forces are known, calculating MA is simply a matter of dividing resistance force by effort force:

MA = \( \frac{F_r}{F_e} \) = \( \frac{4 ft.}{20.0 ft.} \) = 0.2

In this case, the mechanical advantage is less than one meaning that each unit of effort force results in just 0.2 units of resistance force. However, a third class lever like this isn't designed to multiply force like a first class lever. A third class lever is designed to multiply distance and speed at the resistance by sacrificing force at the resistance. Different lever styles have different purposes and multiply forces in different ways.

2 The green box weighs 60 lbs. and a 15 lbs. weight is placed 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?
57% Answer Correctly
3.75 ft.
0 ft.
12 ft.
1.25 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 da, our missing value, and plugging in our variables yields:

da = \( \frac{R_bd_b}{R_a} \) = \( \frac{15 lbs. \times 5 ft.}{60 lbs.} \) = \( \frac{75 ft⋅lb}{60 lbs.} \) = 1.25 ft.

3

When all forces acting on a system cancel each other out, this is called:

80% Answer Correctly

stasis

rest

equilibrium

potential energy
Solution

When a system is stable or balanced (equilibrium) all forces acting on the system cancel each other out. In the case of torque, equilibrium means that the sum of the anticlockwise moments about a center of rotation equal the sum of the clockwise moments.

4

Which of the following is the formula for torque?

61% Answer Correctly

τ = F/r

τ = F/r2

τ = r/F

τ = rF
Solution

Torque measures force applied during rotation: τ = rF.  Torque (τ, the Greek letter tau) = the radius of the lever arm (r) multiplied by the force (F) applied. Radius is measured from the center of rotation or fulcrum to the point at which the perpendicular force is being applied. The resulting unit for torque is newton-meter (N-m) or foot-pound (ft-lb).

5 How much resistance could a 110 lb. effort force lift using a block and tackle pulley that has 10 ropes supporting the resistance?
80% Answer Correctly
1650 lbs.
3300 lbs.
1100 lbs.
1101.5 lbs.
Solution

The mechanical advantage (MA) of a block and tackle pulley is equal to the number of times the effort force changes direction. An easy way to count how many times the effort force changes direction is to count the number of ropes that support the resistance which, in this problem, is 10. With a MA of 10, a 110 lbs. effort force could lift 110 lbs. x 10 = 1100 lbs. resistance.