| Your Results | Global Average | |
|---|---|---|
| Questions | 5 | 5 |
| Correct | 0 | 3.06 |
| Score | 0% | 61% |
Which of the following represents the force a surface exerts when an object presses against it?
mass |
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normal force |
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counter force |
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friction |
Normal force (FN) represents the force a surface exerts when an object presses against it.
| 660 lbs. | |
| 600 lbs. | |
| 592 lbs. | |
| 602 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 75 lbs. effort force could lift 75 lbs. x 8 = 600 lbs. resistance.
A fixed pulley is useful for which of the following?
changing the direction of the input force |
|
multiplying the input distance |
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multiplying the input force |
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changing the direction of the output force |
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.
Two gears are connected and the larger gear drives the smaller gear. The speed of rotation will __________ and the torque will __________.
increase, decrease |
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decrease, decrease |
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decrease, increase |
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increase, increase |
Connected gears of different numbers of teeth are used together to change the rotational speed and torque of the input force. If the smaller gear drives the larger gear, the speed of rotation will be reduced and the torque will increase. If the larger gear drives the smaller gear, the speed of rotation will increase and the torque will be reduced.
| 170% | |
| 42% | |
| 0% | |
| 85% |