ASVAB Mechanical Comprehension Practice Test 428431 Results

Your Results Global Average
Questions 5 5
Correct 0 2.95
Score 0% 59%

Review

1 What is the power output of a 5 hp engine that's 30% efficient?
39% Answer Correctly
825 \( \frac{ft⋅lb}{s} \)
1650 \( \frac{ft⋅lb}{s} \)
206.3 \( \frac{ft⋅lb}{s} \)
275 \( \frac{ft⋅lb}{s} \)
Solution
\( Efficiency = \frac{Power_{out}}{Power_{in}} \times 100 \)
Solving for power out: \( P_{o} = \frac{E \times P_{i}}{100} \)
Knowing that 1 hp = 550 \( \frac{ft⋅lb}{s} \), Pi becomes 5 hp x 550 \( \frac{ft⋅lb}{s} \) = 2750 \( \frac{ft⋅lb}{s} \)
\( P_{o} = \frac{E \times P_{i}}{100} = \frac{30 \times 2750 \frac{ft⋅lb}{s}}{100} \) \( = \frac{82500 \frac{ft⋅lb}{s}}{100} \) = 825 \( \frac{ft⋅lb}{s} \)
2

Tension is a force that does which of the following?

75% Answer Correctly

slows an object

heats up an object

compacts an object

stretches an object
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

Sam can do 50 ft. lb. of work in 2 minutes and 5 seconds. What would Sam have to do to increase his power output?

64% Answer Correctly

do 100 ft. lb. of work in 4 minutes 12 seconds

do the work in 2 minutes

do 25 ft. lb. of work in 2 minutes 5 seconds

do the work in 3 minutes
Solution

Power is the rate of doing work or \(\frac{W}{t}\). To increase power, increase the work being done in the same amount of time or do the same amount of work in less time.

4

Assuming force applied remains constant, which of the following will result in more work being done?

53% Answer Correctly

moving the object with more speed

increasing the coefficient of friction

moving the object with more acceleration

moving the object farther
Solution

Work is accomplished when force is applied to an object: W = Fd where F is force in newtons (N) and d is distance in meters (m). Thus, the more force that must be applied to move an object, the more work is done and the farther an object is moved by exerting force, the more work is done.

5 If the green box weighs 10 lbs. and is 4 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 6 ft.?
62% Answer Correctly
0 lbs.
3.33 lbs.
20 lbs.
6.67 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 = \( \frac{R_ad_a}{d_b} \) = \( \frac{10 lbs. \times 4 ft.}{6 ft.} \) = \( \frac{40 ft⋅lb}{6 ft.} \) = 6.67 lbs.