| Your Results | Global Average | |
|---|---|---|
| Questions | 5 | 5 |
| Correct | 0 | 3.24 |
| Score | 0% | 65% |
A screw is most like which of the following other simple machines?
block and tackle |
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first-class lever |
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wheel and axle |
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inclined plane |
A screw is an inclined plane wrapped in ridges (threads) around a cylinder. The distance between these ridges defines the pitch of the screw and this distance is how far the screw advances when it is turned once. The mechanical advantage of a screw is its circumference divided by the pitch.
Which of the following statements about this pulley configuration is false?
Changes the direction of and multiplies the effort force |
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Mechanical advantage is the number of ropes that support the resistance |
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Only multiplies the effort force |
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This is a block and tackle pulley configuration |
A block and tackle is a combination of one or more fixed pulleys and one or more movable pulleys where the fixed pulleys change the direction of the effort force and the movable pulleys multiply it. The mechanical advantage is equal to the number of times the effort force changes direction and can be increased by adding more pulley wheels to the system. An easy way to find the mechanical advantage of a block and tackle pulley system is to count the number of ropes that support the resistance.
The steering wheel of a car is an example of which type of simple machine?
wheel and axle |
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first-class lever |
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fixed pulley |
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block and tackle |
A wheel and axle uses two different diameter wheels mounted to a connecting axle. Force is applied to the larger wheel and large movements of this wheel result in small movements in the smaller wheel. Because a larger movement distance is being translated to a smaller distance, force is increased with a mechanical advantage equal to the ratio of the diameters of the wheels. An example of a wheel and axle is the steering wheel of a car.
The force required to initally get an object moving is __________ the force required to keep it moving.
opposite |
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lower than |
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the same as |
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higher than |
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?
\(PE = { 1 \over 2} mv^2\) |
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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).