Power : The speed at which a job is performed per unit time is called power. Power is one of the frequently used concepts in daily life. However, the concept of power used in physics and the concept of power we use in daily life are different things. For example, a man who lifts a heavy object is called strong. However, the meaning of power in physics means doing the same work in a short time.
To explain with a more understandable example; Bob carries a 5-pound watermelon he bought from the grocery store in 10 minutes, while his brother Jack carries a 5-pound watermelon in 8 minutes. In this case, Bob is more powerful than Jack.
The speed at which a job is done per unit time is called power.
Power icon: P
Power unit in SI: Watt (W)
Power = (Work Done) / (Duration of Work) ⇒ P = W / t
Power = (Transferred Energy) / (Elapsed time) ⇒ P = ΔE / t
Work or energy is inversely proportional to time and power which is directly proportional to energy. That is, the more work or energy, the greater the power, the more time the smaller the power.
Business unit: Joule (J)
Time unit: Seconds (s)
P = W / t = 1J / 1s = J / s = Watts (W)
Power-related sample questions and solutions
Example 1: An engine is performing 2100 joules in 10 minutes. In this case, how many watts would this engine have?
Solution: Since we were asked to find the power in watts, the job should be in joules and the time should be in seconds. That’s why we turn the minute into seconds.
t = 5.60 = 300 s P = W / t = 2100/300 = 7 watts.
Example 2: How many watts is the engine of 10 joules per second?
P = W / t = 10/1 = 10 watts.
Example 3: How many joules does the engine do in 5 seconds with 20 watts?
If P = W / t, W = P.t = 20.5 = 100 joules.
Example 4: An automobile engine 4000 N force to the car on a 2000-meter road and make it take this path in 50 s. Along the way, the car has a constant, 500 N friction force. In this case, how many watts would the car have for 50 seconds?
Find the net force acting on the car; Fnet = 4000-500 = 3500 N Let’s find the power of the car; P = W / t = RXR / t According to this, P = 3500. 2000/50 P = 700000 watts.