ASVAB Mechanical Comprehension Practice Test 464186 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.92
Score	0%	58%

Review

Lisa lifts a 25 pound box from the floor onto a loading dock 4 ft. off the ground. Sam slides the same box along a ramp to move it up another 4 ft. onto a flatbed truck. Who has done more work?

50% Answer Correctly

	Lisa
	Neither have done any work
	They have done an equal amount of work
	Sam

Solution

Work is force multiplied by distance. Because both Connie and Sam moved the same weight the same distance they have done an equal amount of work. Sam employed the mechnacial advantage of an inclined plane so he exerted less effort to do the work but the amount of work done was still the same.

Which of the following is the formula for gravitational potential energy?

62% Answer Correctly

	\(PE = { 1 \over 2} mg^2\)
	\(PE = { 1 \over 2} mv^2\)
	\(PE = mgh\)
	\(PE = mg^2h\)

Solution

Gravitational potential energy is energy by virtue of gravity. The higher an object is raised above a surface the greater the distance it must fall to reach that surface and the more velocity it will build as it falls. For gravitational potential energy, PE = mgh where m is mass (kilograms), h is height (meters), and g is acceleration due to gravity which is a constant (9.8 m/s²).

Which of these is the formula for force?

77% Answer Correctly

	F = ma
	F = m/a
	F = am²
	F = a/m

Solution

Newton's Second Law of Motion states that "The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object." This Law describes the linear relationship between mass and acceleration when it comes to force and leads to the formula F = ma or force equals mass multiplied by rate of acceleration.

4 What is the power output of a 8 hp engine that's 80% efficient?

40% Answer Correctly

	1760 \( \frac{ft⋅lb}{s} \)
	3520 \( \frac{ft⋅lb}{s} \)
	10560 \( \frac{ft⋅lb}{s} \)
	880 \( \frac{ft⋅lb}{s} \)

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 \( \frac{ft⋅lb}{s} \), P_i becomes 8 hp x 550 \( \frac{ft⋅lb}{s} \) = 4400 \( \frac{ft⋅lb}{s} \)
\( P_{o} = \frac{E \times P_{i}}{100} = \frac{80 \times 4400 \frac{ft⋅lb}{s}}{100} \) \( = \frac{352000 \frac{ft⋅lb}{s}}{100} \) = 3520 \( \frac{ft⋅lb}{s} \)

5 If the green box weighs 75 lbs. and 15 lbs. of force is applied 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?

55% Answer Correctly

	1 ft.
	0.5 ft.
	4 ft.
	3 ft.

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:

R_ad_a = R_bd_b

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 d_a, our missing value, and plugging in our variables yields:

d_a = \( \frac{R_bd_b}{R_a} \) = \( \frac{15 lbs. \times 5 ft.}{75 lbs.} \) = \( \frac{75 ft⋅lb}{75 lbs.} \) = 1 ft.