| Your Results | Global Average | |
|---|---|---|
| Questions | 5 | 5 |
| Correct | 0 | 3.20 |
| Score | 0% | 64% |
The mechanical advantage of a block and tackle is equal to which of the following?
the number of connecting ropes |
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the number of loads |
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the number of pulleys |
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the number of input forces |
Two or more pulleys used together constitute a block and tackle which, unlike a fixed pulley, does impart mechanical advantage as a function of the number of pulleys that make up the arrangement. So, for example, a block and tackle with three pulleys would have a mechanical advantage of three.
A box is resting on a smooth floor. Static friction is present:
only if normal force is present |
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at all times |
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when an attempt is made to move the box |
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if the coefficient of friction is greater than one |
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).
Which of the following is the formula for gravitational potential energy?
\(PE = { 1 \over 2} mg^2\) |
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\(PE = { 1 \over 2} mv^2\) |
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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).
Concurrent forces:
act along the same line of action |
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act in a common plane |
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act in a common dimension |
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pass through a common point |
Collinear forces act along the same line of action, concurrent forces pass through a common point and coplanar forces act in a common plane.
The mechanical advantage of connected gears is proportional to which characteristic of the gears?
speed |
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diameter |
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number of teeth |
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circumference |
The mechanical advantage (amount of change in speed or torque) of connected gears is proportional to the number of teeth each gear has. Called gear ratio, it's the ratio of the number of teeth on the larger gear to the number of teeth on the smaller gear. For example, a gear with 12 teeth connected to a gear with 9 teeth would have a gear ratio of 4:3.