Power
Power is the rate at which energy is used or work is done.
This means that energy equals power 脳 timeTerm that describes the order and duration of events. For example, the Physics lesson was 50 minutes long., or:
\(E = Pt\) with units of joules, watts and seconds.
This applies to all forms of work and all kinds of energy.
Question
A student of mass 64.0 kg runs up four flights of stairs, a total vertical height of 20.0 m, in 32.0 s.
Calculate the gain in potential energy of the student.
Potential energy can be worked out using the equation \({E_p} = mgh\)
\(m = 64.0kg\)
\(g = 9.8N k{g^{- 1}}\)
\(h = 20.0m\)
\({E_p} = mgh\)
\({E_p} = 64.0 \times 9.8\times 20.0\)
\(= 12544 J\)
Question
Calculate the average power of the student.
\(t=32.0s\)
\(E = Pt\)
\(12544 = P\times 32\)
\(P = \frac{12544}{32} = 392\)
The power of the student is 392 W.
Question
Now state any assumption you have made in your calculation.
All of the student's power is used for the vertical climb. The student does not use any other power.
In practice, however, the student's power would be greater than the value calculated since some energy is used in overcoming frictional forces.