| Your Results | Global Average | |
|---|---|---|
| Questions | 5 | 5 |
| Correct | 0 | 2.51 |
| Score | 0% | 50% |
| 9.5 | |
| 12.5 | |
| 19.5 | |
| 6.5 |
The mechanical advantage of a gear train is its gear ratio. The gear ratio (Vr) is the product of the gear ratios between the pairs of meshed gears. Let N represent the number of teeth for each gear:
Vr = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) \( \frac{N_3}{N_4} \) ... \( \frac{N_n}{N_{n+1}} \)
In this problem, we have three gears so the equation becomes:
Vr = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) = \( \frac{26}{14} \) \( \frac{14}{4} \) = \( \frac{26}{4} \) = 6.5
Which of the following statements about this pulley configuration is false?
Mechanical advantage is the number of ropes that support the resistance |
|
This is a block and tackle pulley configuration |
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Only multiplies the effort force |
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Changes the direction of and multiplies the effort force |
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.
Which of the following represents how much two materials resist sliding across each other?
kinetic friction |
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normal friction |
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static friction |
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coefficient of 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 truck is using a rope to pull a car. Tension in the rope is greatest in which of the following places?
near the car |
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near the truck |
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in the middle |
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tension is equal in all parts of the rope |
Tension is a force that stretches or elongates something. When a cable or rope is used to pull an object, for example, it stretches internally as it accepts the weight that it's moving. Although tension is often treated as applying equally to all parts of a material, it's greater at the places where the material is under the most stress.
Which of the following is not a type of structural load?
live load |
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occupancy load |
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dead load |
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wind load |
Dead load is the weight of the building and materials, live load is additional weight due to occupancy or use, snow load is the weight of accumulated snow on a structure and wind load is the force of wind pressures against structure surfaces.