ASVAB Mechanical Comprehension Practice Test 905143 Results

Your Results Global Average
Questions 5 5
Correct 0 3.64
Score 0% 73%

Review

1 A = 6 ft., the green box weighs 20 lbs., and the blue box weighs 25 lbs. What does distance B need to be for this lever to balance?
65% Answer Correctly
4.8 ft.
3 ft.
0 ft.
150 ft.
Solution
In order for this lever to balance, the torque acting on side A must equal the torque acting on side B. Torque is weight x distance from the fulcrum which means that the following must be true for the lever to balance:

fAdA = fBdB

For this problem, the equation becomes:

20 lbs. x 6 ft. = 25 lbs. x dB

dB = \( \frac{20 \times 6 ft⋅lb}{25 lbs.} \) = \( \frac{120 ft⋅lb}{25 lbs.} \) = 4.8 ft.

2

The force amplification achieved by using a tool, mechanical device or machine system is called:

80% Answer Correctly

efficiency

power

work

mechanical advantage
Solution

Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. Such a device utilizes input force and trades off forces against movement to amplify and/or change its direction.

3 If the green box is 5 ft. from the fulcrum and a certain force applied 9 ft. from the fulcrum at the blue arrow balances the lever, what is the mechanical advantage?
61% Answer Correctly
3.6
2.7
1.98
1.8
Solution

Because this lever is in equilibrium, we know that the effort force at the blue arrow is equal to the resistance weight of the green box. For a lever that's in equilibrium, one method of calculating mechanical advantage (MA) is to divide the length of the effort arm (Ea) by the length of the resistance arm (Ra):

MA = \( \frac{E_a}{R_a} \) = \( \frac{9 ft.}{5 ft.} \) = 1.8

When a lever is in equilibrium, the torque from the effort and the resistance are equal. The equation for equilibrium is Rada = Rbdb where a and b are the two points at which effort/resistance is being applied to the lever.

In this problem, Ra and Rb are such that the lever is in equilibrium meaning that some multiple of the weight of the green box is being applied at the blue arrow. For a lever, this multiple is a function of the ratio of the distances of the box and the arrow from the fulcrum. That's why, for a lever in equilibrium, only the distances from the fulcrum are necessary to calculate mechanical advantage.

If the lever were not in equilibrium, you would first have to calculate the forces and distances necessary to put it in equilibrium and then divide Ea by Ra to get the mechanical advantage.

4

The force exerted on an object due to gravity is called:

70% Answer Correctly

density

potential energy

mass

weight
Solution

Mass is an intrinsic property of matter and does not vary. Weight is the force exerted on the mass of an object due to gravity and a specific case of Newton's Second Law of Motion. Replace force with weight and acceleration with acceleration due to gravity on Earth (g) and the result is the formula for weight: W = mg or, substituting for g, weight equals mass multiplied by 9.8 m/s2.

5

The steering wheel of a car is an example of which type of simple machine?

89% Answer Correctly

first-class lever

fixed pulley

block and tackle

wheel and axle
Solution

A wheel and axle uses two different diameter wheels mounted to a connecting axle. Force is applied to the larger wheel and large movements of this wheel result in small movements in the smaller wheel. Because a larger movement distance is being translated to a smaller distance, force is increased with a mechanical advantage equal to the ratio of the diameters of the wheels. An example of a wheel and axle is the steering wheel of a car.