| Your Results | Global Average | |
|---|---|---|
| Questions | 5 | 5 |
| Correct | 0 | 2.72 |
| Score | 0% | 54% |
The standard unit of energy is the:
Horsepower |
|
Volt |
|
Watt |
|
Joule |
The Joule (J) is the standard unit of energy and has the unit \({kg \times m^2} \over s^2\).
| -1 | |
| 8 | |
| 0.88 | |
| 7 |
The mechanical advantage of a wheel and axle is the input radius divided by the output radius:
MA = \( \frac{r_i}{r_o} \)
In this case, the input radius (where the effort force is being applied) is 7 and the output radius (where the resistance is being applied) is 8 for a mechanical advantage of \( \frac{7}{8} \) = 0.88
Which of the following statements about drag is false?
the amount of drag depends on the speed of an object |
|
the amount of drag depends on the shape of an object |
|
drag occurs during movement through a fluid |
|
slower objects experience more drag than faster objects |
Drag is friction that opposes movement through a fluid like liquid or air. The amount of drag depends on the shape and speed of the object with slower objects experiencing less drag than faster objects and more aerodynamic objects experiencing less drag than those with a large leading surface area.
| 2.1 | |
| 0.6 | |
| 1.6 | |
| 0.3 |
Mechanical advantage (MA) is the ratio by which effort force relates to resistance force. If both forces are known, calculating MA is simply a matter of dividing resistance force by effort force:
MA = \( \frac{F_r}{F_e} \) = \( \frac{9 ft.}{15.0 ft.} \) = 0.6
In this case, the mechanical advantage is less than one meaning that each unit of effort force results in just 0.6 units of resistance force. However, a third class lever like this isn't designed to multiply force like a first class lever. A third class lever is designed to multiply distance and speed at the resistance by sacrificing force at the resistance. Different lever styles have different purposes and multiply forces in different ways.
Which of the following is not true of a first-class lever?
decreases distance |
|
increases distance |
|
changes the direction of force |
|
increases force |
A first-class lever is used to increase force or distance while changing the direction of the force. The lever pivots on a fulcrum and, when a force is applied to the lever at one side of the fulcrum, the other end moves in the opposite direction. The position of the fulcrum also defines the mechanical advantage of the lever. If the fulcrum is closer to the force being applied, the load can be moved a greater distance at the expense of requiring a greater input force. If the fulcrum is closer to the load, less force is required but the force must be applied over a longer distance. An example of a first-class lever is a seesaw / teeter-totter.