ASVAB Mechanical Comprehension Practice Test 2588 Results

	Your Results	Global Average
Questions	5	5
Correct	0	3.41
Score	0%	68%

Review

1 If a 25 lbs. weight is placed 9 ft. from the fulcrum at the blue arrow and the green box is 2 ft. from the fulcrum, how much would the green box have to weigh to balance the lever?

61% Answer Correctly

	112.5 lbs.
	225 lbs.
	450 lbs.
	28.13 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 = \( \frac{R_bd_b}{d_a} \) = \( \frac{25 lbs. \times 9 ft.}{2 ft.} \) = \( \frac{225 ft⋅lb}{2 ft.} \) = 112.5 lbs.

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

79% Answer Correctly

	2
	0
	1
	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.

3 How much resistance could a 245 lb. effort force lift using a block and tackle pulley that has 10 ropes supporting the resistance?

81% Answer Correctly

	2450 lbs.
	2453 lbs.
	1225 lbs.
	2205 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 10. With a MA of 10, a 245 lbs. effort force could lift 245 lbs. x 10 = 2450 lbs. resistance.

4 If A = 7 ft. and the green box weighs 30 lbs. what is the torque acting on the A side of this lever?

75% Answer Correctly

	210 ft⋅lb
	105 ft⋅lb
	420 ft⋅lb
	70 ft⋅lb

Solution

For a lever, torque is weight x distance from the fulcrum which, in this case, is: 30 ft. x 7 lbs. = 210 ft⋅lb

Which of the following represents the force a surface exerts when an object presses against it?

48% Answer Correctly

	counter force
	mass
	friction
	normal force

Solution

Normal force (F_N) represents the force a surface exerts when an object presses against it.