ASVAB Mechanical Comprehension Practice Test 276103 Results

Your Results Global Average
Questions 5 5
Correct 0 3.02
Score 0% 60%

Review

1 If the green box weighs 10 lbs. and is 3 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 5 ft.?
62% Answer Correctly
2 lbs.
6 lbs.
50 lbs.
3 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 = \( \frac{R_ad_a}{d_b} \) = \( \frac{10 lbs. \times 3 ft.}{5 ft.} \) = \( \frac{30 ft⋅lb}{5 ft.} \) = 6 lbs.

2

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

80% Answer Correctly

stasis

potential energy

rest

equilibrium
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.

3

Which of the following represents how much two materials resist sliding across each other?

53% Answer Correctly

kinetic friction

coefficient of friction

static friction

normal friction
Solution

Coefficient of friction (μ) represents how much two materials resist sliding across each other.  Smooth surfaces like ice have low coefficients of friction while rough surfaces like concrete have high μ.

4

A truck is using a rope to pull a car. Tension in the rope is greatest in which of the following places?

50% Answer Correctly

near the truck

near the car

tension is equal in all parts of the rope

in the middle
Solution

Tension is a force that stretches or elongates something. When a cable or rope is used to pull an object, for example, it stretches internally as it accepts the weight that it's moving. Although tension is often treated as applying equally to all parts of a material, it's greater at the places where the material is under the most stress.

5

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

90 lbs

0.83 lbs

45 lbs

810 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