Power
Hey students here we are going to learn about the concept of power. Consider the following examples to understand concept of power in detail.
Imagine your teacher asked you to lift a heavy cupboard and keep is outside, he selected four boys from std. X and four from std.VII. Can you guess which group of boys will do the work in less time? Definitely the boys from std. X will do it earlier as they have more strength than that of students from std. VII. Here we can conclude that strength can be described with work and time.
Power is defined as rate of doing work. Thus if someone takes less time to do the certain work, then we can say that the power of that person/machine is more.
If, W = work done
t = time required
Then, Power = work/time
∴ P = W/t
SI unit of power is J/s or watt (W)
Power also can be expressed in kilowatt (kW) and horse power (hp),
where 1 kW = 1000 watt.
And 1 horsepower = 746 watt.
Following are some numerical which will give detail about power
Ex: 1) A student takes time of 10 s to shift the table from one corner of class by 5 m. Force required to shift the table is 100 N. Find the power of student.
Ans: here,
F = 100 N
s = 5 m
t = 10 s
Power = work/time
∴ P = W/t
But, W = F.s
∴ P = (F.s)/t
∴ P = (100×5)/10
∴ P = 10 × 5
∴ P = 50 W
Ex: 2) Power of 10 kilowatt is required by engine to pull a trolley of mass 250 kg in time 20 seconds. Find the displacement of trolley. (Use g=10 m/s2)
Ans: here,
P = 10 kW = 10000 watt
t = 20 s
m = 250 kg
Force required = Weight of trolley
F = mg =250 ×10 =2500 N
Power = work/time
∴ P = W/t
But, W = F.s
∴ P = (F.s)/t
∴ 10000 = (2500×s)/20
∴ 10000 = 125 × s
∴ s = 10000/125
∴ s = 80 m