ASVAB Mechanical Comprehension Practice Test 127029 Results

Your Results Global Average
Questions 5 5
Correct 0 2.67
Score 0% 53%

Review

1

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

48% Answer Correctly

Only multiplies the effort force

This is a block and tackle pulley configuration

Changes the direction of and multiplies the effort force

Mechanical advantage is the number of ropes that support the resistance
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.

2

The measure of how much of the power put into a machine is turned into movement or force is called:

56% Answer Correctly

power

efficiency

mechanical advantage

force multiplication
Solution

The efficiency of a machine describes how much of the power put into the machine is turned into movement or force. A 100% efficient machine would turn all of the input power into output movement or force. However, no machine is 100% efficient due to friction, heat, wear and other imperfections that consume input power without delivering any output.

3 If A = 10 ft., B = 3 ft., C = 6 ft., the green box weighs 25 lbs. and the blue box weighs 35 lbs., what does the orange box have to weigh for this lever to balance?
44% Answer Correctly
0 lbs.
72.5 lbs.
96.67 lbs.
24.17 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:

fAdA = fBdB + fCdC

For this problem, this equation becomes:

25 lbs. x 10 ft. = 35 lbs. x 3 ft. + fC x 6 ft.

250 ft. lbs. = 105 ft. lbs. + fC x 6 ft.

fC = \( \frac{250 ft. lbs. - 105 ft. lbs.}{6 ft.} \) = \( \frac{145 ft. lbs.}{6 ft.} \) = 24.17 lbs.

4 If 60 lbs. of force is applied 9 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
0 lbs.
6 lbs.
22.5 lbs.
90 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:

Rada = Rbdb

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

Ra = \( \frac{R_bd_b}{d_a} \) = \( \frac{60 lbs. \times 9 ft.}{6 ft.} \) = \( \frac{540 ft⋅lb}{6 ft.} \) = 90 lbs.

5

A wedge converts force applied to its blunt end into force __________ its inclined surface.

57% Answer Correctly

along

perpendicular to

opposite to

parallel to
Solution

The wedge is a moving inclined plane that is used to lift, hold, or break apart an object. A wedge converts force applied to its blunt end into force perpendicular to its inclined surface. In contrast to a stationary plane where force is applied to the object being moved, with a wedge the object is stationary and the force is being applied to the plane. Examples of a wedge include knives and chisels.