ASVAB Mechanical Comprehension Practice Test 11294 Results

	Your Results	Global Average
Questions	5	5
Correct	0	2.77
Score	0%	55%

Review

1 What is the mechanical advantage of this inclined plane if the length of the ramp is 30 ft. and the height of the green box is 6 ft.?

82% Answer Correctly

	13
	7
	10
	5

Solution

The mechanical advantage (MA) of an inclined plane is the effort distance divided by the resistance distance. In this case, the effort distance is the length of the ramp and the resistance distance is the height of the green box:

MA = \( \frac{d_e}{d_r} \) = \( \frac{30 ft.}{6 ft.} \) = 5

2 If A = 10 ft., B = 2 ft., C = 6 ft., the green box weighs 40 lbs. and the blue box weighs 50 lbs., what does the orange box have to weigh for this lever to balance?

44% Answer Correctly

	80 lbs.
	4 lbs.
	100 lbs.
	50 lbs.

Solution

In order for this lever to balance, the torque acting on each side of the fulrum must be equal. So, the torque produced by A must equal the torque produced by B and C. Torque is weight x distance from the fulcrum which means that the following must be true for the lever to balance:

f_Ad_A = f_Bd_B + f_Cd_C

For this problem, this equation becomes:

40 lbs. x 10 ft. = 50 lbs. x 2 ft. + f_C x 6 ft.

400 ft. lbs. = 100 ft. lbs. + f_C x 6 ft.

f_C = \( \frac{400 ft. lbs. - 100 ft. lbs.}{6 ft.} \) = \( \frac{300 ft. lbs.}{6 ft.} \) = 50 lbs.

3 The radius of the axle is 7, the radius of the wheel is 12, and the blue box weighs 100 lbs. What is the effort force necessary to balance the load?

53% Answer Correctly

	12 lbs.
	58.48 lbs.
	13.71 lbs.
	84 lbs.

Solution

The mechanical advantage of a wheel and axle is the input radius divided by the output radius:

MA = \( \frac{r_i}{r_o} \)

In this case, the input radius (where the effort force is being applied) is 12 and the output radius (where the resistance is being applied) is 7 for a mechanical advantage of \( \frac{12}{7} \) = 1.71

MA = \( \frac{load}{effort} \) so effort = \( \frac{load}{MA} \) = \( \frac{100 lbs.}{1.71} \) = 58.48 lbs.

A truck is using a rope to pull a car. Tension in the rope is greatest in which of the following places?

50% Answer Correctly

	tension is equal in all parts of the rope
	near the car
	in the middle
	near the truck

Solution

Tension is a force that stretches or elongates something. When a cable or rope is used to pull an object, for example, it stretches internally as it accepts the weight that it's moving. Although tension is often treated as applying equally to all parts of a material, it's greater at the places where the material is under the most stress.

Which of the following statements about this pulley configuration is false?

48% Answer Correctly

	This is a block and tackle pulley configuration
	Only multiplies the effort force
	Mechanical advantage is the number of ropes that support the resistance
	Changes the direction of and multiplies the effort force

Solution

A block and tackle is a combination of one or more fixed pulleys and one or more movable pulleys where the fixed pulleys change the direction of the effort force and the movable pulleys multiply it. The mechanical advantage is equal to the number of times the effort force changes direction and can be increased by adding more pulley wheels to the system. An easy way to find the mechanical advantage of a block and tackle pulley system is to count the number of ropes that support the resistance.