| Your Results | Global Average | |
|---|---|---|
| Questions | 5 | 5 |
| Correct | 0 | 3.10 |
| Score | 0% | 62% |
A wedge is most similar to what other type of simple machine?
second-class lever |
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third-class lever |
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inclined plane |
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first-class lever |
The wedge is a moving inclined plane that is used to lift, hold, or break apart an object. A wedge converts force applied to its blunt end into force perpendicular to its inclined surface. In contrast to a stationary plane where force is applied to the object being moved, with a wedge the object is stationary and the force is being applied to the plane. Examples of a wedge include knives and chisels.
Which of the following is not a type of structural load?
occupancy load |
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dead load |
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wind load |
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live 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.
Which of the following surfaces would have the highest coefficient of friction?
concrete |
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steel |
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ice |
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marble |
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.
| 39 ft. | |
| 6.5 ft. | |
| 9 ft. | |
| 13 ft. |
To balance this lever the torques at the green box and the blue arrow must be equal. Torque is weight x distance from the fulcrum so the equation for equilibrium is:
Rada = Rbdb
where a represents the green box and b the blue arrow, R is resistance (weight/force) and d is the distance from the fulcrum.Solving for db, our missing value, and plugging in our variables yields:
db = \( \frac{R_ad_a}{R_b} \) = \( \frac{65 lbs. \times 7 ft.}{35 lbs.} \) = \( \frac{455 ft⋅lb}{35 lbs.} \) = 13 ft.
For any given surface, the coefficient of static friction is ___________ the coefficient of kinetic friction.
higher than |
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opposite |
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lower than |
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equal to |
For any given surface, the coefficient of static friction is higher than the coefficient of kinetic friction. More force is required to initally get an object moving than is required to keep it moving. Additionally, static friction only arises in response to an attempt to move an object (overcome the normal force between it and the surface).