| Your Results | Global Average | |
|---|---|---|
| Questions | 5 | 5 |
| Correct | 0 | 3.40 |
| Score | 0% | 68% |
| 14.5 | |
| 3.8 | |
| 15 | |
| 7.5 |
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 = \( \frac{N_1}{N_2} \) \( \frac{N_2}{N_3} \) = \( \frac{30}{14} \) \( \frac{14}{4} \) = \( \frac{30}{4} \) = 7.5
Which of the following is the formula for torque?
τ = rF |
|
τ = r/F |
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τ = F/r |
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τ = F/r2 |
Torque measures force applied during rotation: τ = rF. Torque (τ, the Greek letter tau) = the radius of the lever arm (r) multiplied by the force (F) applied. Radius is measured from the center of rotation or fulcrum to the point at which the perpendicular force is being applied. The resulting unit for torque is newton-meter (N-m) or foot-pound (ft-lb).
A ramp is an example of which kind of simple machine?
wedge |
|
inclined plane |
|
none of these |
|
first-class lever |
An inclined plane is a simple machine that reduces the force needed to raise an object to a certain height. Work equals force x distance and, by increasing the distance that the object travels, an inclined plane reduces the force necessary to raise it to a particular height. In this case, the mechanical advantage is to make the task easier. An example of an inclined plane is a ramp.
What type of load doesn't create specific stress points or vary with time?
concentrated load |
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impact load |
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static uniformly distributed load |
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non-uniformly distributed load |
A concentrated load acts on a relatively small area of a structure, a static uniformly distributed load doesn't create specific stress points or vary with time, a dynamic load varies with time or affects a structure that experiences a high degree of movement, an impact load is sudden and for a relatively short duration and a non-uniformly distributed load creates different stresses at different locations on a structure.
Which of the following surfaces would have the lowest coefficient of friction?
concrete |
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tile |
|
ice |
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leather |
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.