Power
In this article we are going to learn about power relate, with calculation, power to work done and time taken, using appropriate examples (P = W/t), recall and use the equation P = W/t = E/t in simple systems.
Definition of terms:
Power: is the rate of work done and the rate of energy tranferred. The more work is done in short period of time the more power, and the more energy is transferred in short period of time the more power. The unit of power is watt (W).
Calculations of power:
We can calculate power in relation with the work done and the energy transferred by using these equations:
P = W/t (In relation with work done.)
WHERE:
P is power.
W is the work done.
t is the time taken.
P = E/t (In relation with energy transferred.)
WHERE:
P is power.
E is the energy transferred.
t is the time taken.
So, we can see that in these two equations we both have variable P (power) and P = P. Therefore, we can conlude that: W/t = E/t.
Worked example:
Question: A science student transferred energy of 60 J to lift a box of science text books in 0.5 minutes. Calcute the power of the student.
Solution: First step; We should list our known and unknown variables.
P = ?
E = 60 J
t = 0.5 min
Second step; We should choose the right equation and place the variables but we must convert 0.5 minutes to seconds. 1 min = 60 s and 0.5 min = 30 s.
Our formula: P = E/t
P = E/t
P = 60 J/30 s
P = 2 W
The power of the student is 2 W and if we were asked to calculate the work done, we know that the work done is the same as energy transferred and is 60 J (W = E).