| Your Results | Global Average | |
|---|---|---|
| Questions | 5 | 5 |
| Correct | 0 | 3.14 |
| Score | 0% | 63% |
Power is the rate at which:
friction is overcome |
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work is done |
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input force is transferred to output force |
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potential energy is converted into kinetic energy |
Power is the rate at which work is done, P = w/t, or work per unit time. The watt (W) is the unit for power and is equal to 1 joule (or newton-meter) per second. Horsepower (hp) is another familiar unit of power used primarily for rating internal combustion engines. 1 hp equals 746 watts.
Which of the following represents how much two materials resist sliding across each other?
coefficient of friction |
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static friction |
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normal friction |
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kinetic friction |
Coefficient of friction (μ) represents how much two materials resist sliding across each other. Smooth surfaces like ice have low coefficients of friction while rough surfaces like concrete have high μ.
A fixed pulley has a mechanical advantage of:
0 |
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2 |
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1 |
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-1 |
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 __________.
decrease, increase |
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decrease, decrease |
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increase, decrease |
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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.
| 0 ft⋅lb | |
| 12 ft⋅lb | |
| 38 ft⋅lb | |
| 114 ft⋅lb |