| Your Results | Global Average | |
|---|---|---|
| Questions | 5 | 5 |
| Correct | 0 | 2.79 |
| Score | 0% | 56% |
Which of the following is the formula for gravitational potential energy?
\(PE = { 1 \over 2} mv^2\) |
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\(PE = { 1 \over 2} mg^2\) |
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\(PE = mg^2h\) |
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\(PE = mgh\) |
Gravitational potential energy is energy by virtue of gravity. The higher an object is raised above a surface the greater the distance it must fall to reach that surface and the more velocity it will build as it falls. For gravitational potential energy, PE = mgh where m is mass (kilograms), h is height (meters), and g is acceleration due to gravity which is a constant (9.8 m/s2).
A wedge converts force applied to its blunt end into force __________ its inclined surface.
along |
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opposite to |
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parallel to |
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perpendicular to |
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.
Lisa lifts a 25 pound box from the floor onto a loading dock 4 ft. off the ground. Sam slides the same box along a ramp to move it up another 4 ft. onto a flatbed truck. Who has done more work?
They have done an equal amount of work |
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Lisa |
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Sam |
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Neither have done any work |
Work is force multiplied by distance. Because both Connie and Sam moved the same weight the same distance they have done an equal amount of work. Sam employed the mechnacial advantage of an inclined plane so he exerted less effort to do the work but the amount of work done was still the same.
Normal force is generally equal to the __________ of an object.
density |
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weight |
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coefficient of friction |
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mass |
Normal force arises on a flat horizontal surface in response to an object's weight pressing it down. Consequently, normal force is generally equal to the object's weight.
| 0.35 | |
| 3.7 | |
| 0.7 | |
| -2.3 |
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 = \( \frac{F_r}{F_e} \) = \( \frac{6 ft.}{8.57 ft.} \) = 0.7
In this case, the mechanical advantage is less than one meaning that each unit of effort force results in just 0.7 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.