ASVAB Mechanical Comprehension Practice Test 563920 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.34
Score	0%	67%

Review

On Earth, acceleration due to gravity (g) is approximately __________.

81% Answer Correctly

	1 m/s
	9.8 m/s²
	1 m/s²
	6.67 x 10^-11 m/s²

Solution

Newton's Law of Univeral Gravitation defines the general formula for the attraction of gravity between two objects: \(\vec{F_{g}} = { Gm_{1}m_{2} \over r^2}\) . In the specific case of an object falling toward Earth, the acceleration due to gravity (g) is approximately 9.8 m/s².

The mechanical advantage of a third class lever is always:

37% Answer Correctly

	greater than one
	less than one
	not equal to one
	equal to one

Solution

A third class lever is designed to multiply distance and speed at the expense of effort force. Because the effort force is greater than the resistance, the mechanical advantage of a third class lever is always less than one.

An example of a third class lever is a broom. The fulcrum is at your hand on the end of the broom, the effort force is your other hand in the middle, and the resistance is at the bottom bristles. The effort force of your hand in the middle multiplies the distance and speed of the bristles at the bottom but at the expense of producing a brushing force that's less than the force you're applying with your hand.

3 If A = 9 ft. and the green box weighs 10 lbs. what is the torque acting on the A side of this lever?

75% Answer Correctly

	90 ft⋅lb
	270 ft⋅lb
	22 ft⋅lb
	30 ft⋅lb

Solution

For a lever, torque is weight x distance from the fulcrum which, in this case, is: 10 ft. x 9 lbs. = 90 ft⋅lb

4 If the force applied at the blue arrow over 7 ft. moves the green box 0.78 ft., what is the mechanical advantage of this lever?

56% Answer Correctly

	9
	27
	8.1
	13.5

Solution

Mechanical advantage (MA) can be calculated knowing only the distance the effort (blue arrow) moves and the distance the resistance (green box) moves. The equation is:

MA = \( \frac{E_d}{R_d} \)

where E_d is the effort distance and R_d is the resistance distance. For this problem, the equation becomes:

MA = \( \frac{7 ft.}{0.78 ft.} \) = 9

You might be wondering how having an effort distance of 9 times the resistance distance is an advantage. Remember the principle of moments. For a lever in equilibrium the effort torque equals the resistance torque. Because torque is force x distance, if the effort distance is 9 times the resistance distance, the effort force must be \( \frac{1}{9} \) the resistance force. You're trading moving 9 times the distance for only having to use \( \frac{1}{9} \) the force.

The force required to initally get an object moving is __________ the force required to keep it moving.

76% Answer Correctly

	higher than
	lower than
	opposite
	the same as

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).