ASVAB Mechanical Comprehension Practice Test 392384 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.21
Score	0%	64%

Review

Which of these is the formula for kinetic energy?

68% Answer Correctly

	\(KE = mgh\)
	\(KE = {m \over v^2 }\)
	\(KE = {1 \over 2}mv^2\)
	\(KE = {1 \over 2}mh^2\)

Solution

Kinetic energy is the energy of movement and is a function of the mass of an object and its speed: \(KE = {1 \over 2}mv^2\) where m is mass in kilograms, v is speed in meters per second, and KE is in joules. The most impactful quantity to kinetic energy is velocity as an increase in mass increases KE linearly while an increase in speed increases KE exponentially.

2 If 35 lbs. of force is applied 8 ft. from the fulcrum at the blue arrow and the green box is 6 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?

62% Answer Correctly

	4 lbs.
	23.33 lbs.
	0 lbs.
	46.67 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:

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

R_a = \( \frac{R_bd_b}{d_a} \) = \( \frac{35 lbs. \times 8 ft.}{6 ft.} \) = \( \frac{280 ft⋅lb}{6 ft.} \) = 46.67 lbs.

3 How much resistance could a 65 lb. effort force lift using a block and tackle pulley that has 6 ropes supporting the resistance?

81% Answer Correctly

	585 lbs.
	429 lbs.
	390 lbs.
	130 lbs.

Solution

The mechanical advantage (MA) of a block and tackle pulley is equal to the number of times the effort force changes direction. An easy way to count how many times the effort force changes direction is to count the number of ropes that support the resistance which, in this problem, is 6. With a MA of 6, a 65 lbs. effort force could lift 65 lbs. x 6 = 390 lbs. resistance.

4 If the handles of a wheelbarrow are 2.0 ft. from the wheel axle, how many pounds of force must you exert to lift the handles if it's carrying a 150 lbs. load concentrated at a point 0.5 ft. from the axle?

52% Answer Correctly

	0
	37.5
	21.9
	75

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: F_ed_e = F_rd_r. In this problem we're looking for effort force:
\( F_e = \frac{F_r d_r}{d_e} \)
\( F_e = \frac{150 \times 0.5}{2.0} \)
\( F_e = \frac{75.0}{2.0} \)
\( F_e = 37.5 \)

Which of the following will increase the mechanical advantage of this inclined plane?

59% Answer Correctly

	lengthen the ramp
	lower the force acting at the blue arrow
	shorten the ramp
	increase the force acting at the blue arrow

Solution

The mechanical advantage (MA) of an inclined plane is the effort distance divided by the resistance distance. In order to increase mechanical advantage, this ratio must increase which means making the effort distance longer and this can be accomplished by lengthening the length of the ramp.