ASVAB Mechanical Comprehension Practice Test 461648 Results

Your Results Global Average
Questions 5 5
Correct 0 3.27
Score 0% 65%

Review

1

Two or more pulleys used together are called:

71% Answer Correctly

gears

wheel and axle

block and tackle

third-class lever
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.

2 If the green box weighs 65 lbs. and is 1 ft. from the fulcrum, how far from the fulcrum would a 40 lbs. weight need to be placed to balance the lever?
61% Answer Correctly
0.41 ft.
1.63 ft.
3.25 ft.
0.54 ft.
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:

Rada = Rbdb

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

db = \( \frac{R_ad_a}{R_b} \) = \( \frac{65 lbs. \times 1 ft.}{40 lbs.} \) = \( \frac{65 ft⋅lb}{40 lbs.} \) = 1.63 ft.

3 If you lift a 47 lbs. rock 40 ft. from the ground, how much work have you done?
71% Answer Correctly
1880 ft⋅lb
87 ft⋅lb
920 ft⋅lb
0 ft⋅lb
Solution
Work is force times distance. In this case, the force is the weight of the rock so:
\( W = F \times d \)
\( W = 47 \times 40 \)
\( W = 1880 \)
4

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

48% Answer Correctly

Only multiplies the effort force

Mechanical advantage is the number of ropes that support the resistance

This is a block and tackle pulley configuration

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.

5 If A = 3 ft. and the green box weighs 40 lbs. what is the torque acting on the A side of this lever?
75% Answer Correctly
60 ft⋅lb
120 ft⋅lb
360 ft⋅lb
40 ft⋅lb
Solution
For a lever, torque is weight x distance from the fulcrum which, in this case, is: 40 ft. x 3 lbs. = 120 ft⋅lb