Last updated on May 6th, 2023 at 06:18 am
In this post, we will define Power (in physics), and list down different formulas of power for class 9. We will also solve a sample numerical using the power formula and concept.
What is Power Class 9 – Physics
Power is the rate at which work is done or the rate at which energy is supplied or used. Like work and energy, power is also a scalar quantity.
The SI unit for power is Joules per second (Js-1), which is defined to be a Watt (W).
So 1 W = 1 J/s. There are other popular units like Kilowatt and horsepower. 1 kilowatt = 1000 Watt and 1 Horsepower = 746 Watt.
Power formula class 9
When we define power as the rate of work done or rate of energy supplied (or used) we get the following formulas:
Average Power formula
Average Power = Work done during some time interval / Duration of time interval ……………… (1)
Average Power = Total Energy supplied or used during some time interval / Duration of time interval ………… (2)
Instantaneous Power formula
The rate at which work is done might not be constant. We define instantaneous power P as the quotient in Eq. (1) as Δt approaches zero:
Numerical problem solved using the power formula
A box with a mass of 30 kg can be lifted by a light rope threaded through a smooth pulley.
(a) If the box is lifted at a constant speed from the ground to a height of 2.0 m in 4.0 s, what is the power required?
(b) If the box is lifted with a constant acceleration of 1.5 m/s2 from rest to a height of 3.0 m above the floor, what is the power required? Take g, the gravitational field strength as 10 N/kg.