ASVAB Mechanical Comprehension Practice Test 577457 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.16
Score	0%	63%

Review

1 If the green box weighs 45 lbs. and 40 lbs. of force is applied 1 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

	0.89 ft.
	0.3 ft.
	0.44 ft.
	1.78 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 = \( \frac{R_bd_b}{R_a} \) = \( \frac{40 lbs. \times 1 ft.}{45 lbs.} \) = \( \frac{40 ft⋅lb}{45 lbs.} \) = 0.89 ft.

Which of these will have the most impact on the kinetic energy of an object?

54% Answer Correctly

	its speed
	its direction
	its weight
	its mass

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.

Which of these is the formula for kinetic energy?

67% Answer Correctly

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

Solution

4 If a 60 lbs. weight is placed 3 ft. from the fulcrum at the blue arrow and the green box is 4 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?

61% Answer Correctly

	11.25 lbs.
	45 lbs.
	15 lbs.
	22.5 lbs.

Solution

To balance this lever the torques on each side of the fulcrum 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 left side of the fulcrum and b the right, R is resistance (weight) and d is the distance from the fulcrum.

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

R_a = \( \frac{R_bd_b}{d_a} \) = \( \frac{60 lbs. \times 3 ft.}{4 ft.} \) = \( \frac{180 ft⋅lb}{4 ft.} \) = 45 lbs.

A block and tackle with four pulleys would have a mechanical advantage of:

79% Answer Correctly

	0
	1
	2
	4

Solution

Two or more pulleys used together constitute a block and tackle which, unlike a fixed pulley, does impart mechanical advantage as a function of the number of pulleys that make up the arrangement. So, for example, a block and tackle with three pulleys would have a mechanical advantage of three.