| Your Results | Global Average | |
|---|---|---|
| Questions | 5 | 5 |
| Correct | 0 | 3.55 |
| Score | 0% | 71% |
| 717 lbs. | |
| 721.5 lbs. | |
| 1080 lbs. | |
| 720 lbs. |
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 8. With a MA of 8, a 90 lbs. effort force could lift 90 lbs. x 8 = 720 lbs. resistance.
Specific gravity is a comparison of the density of an object with the density of:
carbon |
|
oil |
|
air |
|
water |
Specific gravity is the ratio of the density of equal volumes of a substance and water and is measured by a hyrdometer.
The mechanical advantage of a block and tackle is equal to which of the following?
the number of pulleys |
|
the number of loads |
|
the number of input forces |
|
the number of connecting ropes |
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 | |
| 5 | |
| 7 | |
| 5.5 |
The mechanical advantage (MA) of a wedge is its length divided by its thickness:
MA = \( \frac{l}{t} \) = \( \frac{25 in.}{5 in.} \) = 5
A fixed pulley has a mechanical advantage of:
0 |
|
1 |
|
-1 |
|
2 |
A fixed pulley is used to change the direction of a force and does not multiply the force applied. As such, it has a mechanical advantage of one. The benefit of a fixed pulley is that it can allow the force to be applied at a more convenient angle, for example, pulling downward or horizontally to lift an object instead of upward.