| Your Results | Global Average | |
|---|---|---|
| Questions | 5 | 5 |
| Correct | 0 | 3.15 |
| Score | 0% | 63% |
A ramp is an example of which kind of simple machine?
none of these |
|
inclined plane |
|
first-class lever |
|
wedge |
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.
A fixed pulley is useful for which of the following?
multiplying the input force |
|
multiplying the input distance |
|
changing the direction of the output force |
|
changing the direction of the input force |
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.
Power is the rate at which:
input force is transferred to output force |
|
potential energy is converted into kinetic energy |
|
friction is overcome |
|
work is done |
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.
A shovel is an example of which class of lever?
a shovel is not a lever |
|
third |
|
first |
|
second |
A third-class lever is used to increase distance traveled by an object in the same direction as the force applied. The fulcrum is at one end of the lever, the object at the other, and the force is applied between them. This lever does not impart a mechanical advantage as the effort force must be greater than the load but does impart extra speed to the load. Examples of third-class levers are shovels and tweezers.
A box is resting on a smooth floor. Static friction is present:
if the coefficient of friction is greater than one |
|
only if normal force is present |
|
at all times |
|
when an attempt is made to move the box |
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).