ASVAB Mechanical Comprehension Practice Test 205478 Results

Your Results Global Average
Questions 5 5
Correct 0 2.83
Score 0% 57%

Review

1 How much work can a 5 hp engine do in 3 seconds?
52% Answer Correctly
1 ft⋅lb
20 ft⋅lb
0 ft⋅lb
8250 ft⋅lb
Solution
Horsepower (hp) is a common measure of power output for complex machines. By definition, a 1 hp machine does 550 ft⋅lb of work in 1 second: 1 hp = 550 ft⋅lb/s. Substituting the variables for this problem gives us:
\( W = 5 hp \times 550 \frac{ft⋅lb}{s} \times 3s = 8250 ft⋅lb \)
2

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

in the middle

near the car

near the truck

tension is equal in all parts of the rope
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.

3

The mechanical advantage of a wheel and axle is equal to the:

61% Answer Correctly

difference in the diameters of the wheels

ratio of the diameters of the wheels

difference in the lengths of the axles

length of the 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.

4

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

59% Answer Correctly

when an attempt is made to move the box

only if normal force is present

at all times

if the coefficient of friction is greater than one
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).

5 If the green box weighs 30 lbs. and is 5 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 8 ft.?
62% Answer Correctly
18.75 lbs.
0 lbs.
4.69 lbs.
240 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 = \( \frac{R_ad_a}{d_b} \) = \( \frac{30 lbs. \times 5 ft.}{8 ft.} \) = \( \frac{150 ft⋅lb}{8 ft.} \) = 18.75 lbs.