AP Physics C: Mechanics : Power
研究概念,例子问题&解释for AP Physics C: Mechanics
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Example Questions
Example Question #5 :Work, Energy, And Power
When riding your bicycle, you have a maximum power output of 500W. As you approach a hill, you shift into first gear, applying a torque of
Power is determined by calculating the work output per unit time. In this case, power will be the product of torque and angular velocity:
We are given values for our torque and our power output, allowing us to solve for the angualr velocity. Keep in mind that the power output is going to be 50% of the maximum.
Example Question #1 :Work, Energy, And Power
起重机升降机质量50公斤一箱。社区再投资法案te is raised at a constant velocity for ten seconds and and moves a vertical distance upwards of 20m. What power is being supplied to the crane during this time?
For this problem we can calculate the power as the product of force and velocity:
First, we need to find the velocity:
我们的力量将等于箱的重量:
Now, we can solve for power:
Example Question #1 :Work, Power, And Diagrams
A person is moving boxes up the stairs in their new home. They have two identical boxes, with same the size and mass. The first box is easy to carry up the stairs. When moving the second box, the person is more tired and moves more slowly. Which statement accurately describes the work and power between the two trials?
工作保持不变;功率下降
Work increases; power decreases
Work decreases; power stay the same
Work increases; power increases
工作保持不变;power increases
工作保持不变;功率下降
Because the boxes are the same mass and are moving the same distance, the work done will remain the same between the two instances. Work does not depend on time:
However, when carrying the second box, the person moves more slowly. The overall time increases, which leads to a decrease in power.
Example Question #1 :Work, Energy, And Power
What power is required to lift a 25kg box 5.76m off the ground in fifteen seconds?
The definition of power is:
The work done on the box to lift it is required in order to overcome the force of gravity. If we can find the force of gravity on the object, we can calculate the net force. The force of gravity on any object near the Earth's surface is:
The definition of work is:
We can substitute the force of gravity for the net force, resulting in the equation:
Substituting this into our power equation, we find:
Plugging in our given values and constants, we find:
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