| Your Results | Global Average | |
|---|---|---|
| Questions | 5 | 5 |
| Correct | 0 | 3.35 |
| Score | 0% | 67% |
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?
Lisa |
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Sam |
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Neither have done any work |
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They have done an equal amount of 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.
Which of the following represents how much two materials resist sliding across each other?
normal friction |
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static friction |
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kinetic friction |
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coefficient of friction |
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.
An object's resistance to changes in direction is known as:
weight |
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inertia |
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mass |
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kinetic energy |
The more mass a substance has the more force is required to move it or to change its direction. This resistance to changes in direction is known as inertia.
| 841.5 lbs. | |
| 420 lbs. | |
| 833 lbs. | |
| 840 lbs. |
The mechanical advantage (MA) of a block and tackle pulley is equal to the number of times the effort force changes direction. An easy way to count how many times the effort force changes direction is to count the number of ropes that support the resistance which, in this problem, is 8. With a MA of 8, a 105 lbs. effort force could lift 105 lbs. x 8 = 840 lbs. resistance.
The mass of an object correlates to the size of the object but ultimately depends on:
gravity |
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the object's potential energy |
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the object's weight |
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the object's density |
Mass is a measure of the amount of matter in an object. In general, larger objects have larger mass than smaller objects but mass ultimately depends on how compact (dense) a substance is.