Work
Hello students, in this article we are going to deal with the important article i.e. work. We are familiar with concept of force. Force has ability to change the position of a body. Force can change the state of object from one place to another and produces displacement. Remember in your childhood you must have played with toy cart made with empty match box. In that case we had attached a thread to pull the toy cart in desired direction. When you pulled it, it gets displaced i.e. work is done.
Work is defined as the product of force and displacement.
∴ W = F.s
SI unit of work is N-m or joule (J)
See the above diagram, in which a toy cart is moved by distance‘s’ with force F. But in this case the angle between force and displacement is ‘θ’ then the component of force along the direction of displacement will be,
∴F’ = F cosθ
In this case, the work done is given as,
∴W = F’.s
∴W = F cos θ.s
∴W = F s cos θ
From the above explanation work can be of following types:
1) Positive work: When the displacement and applied force are along same direction, the work done is said to be positive.
Here θ = 00 → ∴ W = F s cos 00 = F s
2) Negative work: When the displacement and applied force are in opposite direction, the work done is said to be negative.
Here θ = 1800 → ∴ W = F s cos 1800 = – F s
3) Zero: When the displacement and applied force perpendicular to each other, work is said to be zero work.
Here θ = 900 → ∴ W = F s cos 900 = 0
Consider some of the numerical, which will illustrate the work in more detail.
Ex:1) Force of 25 N is required to move a table in classroom by 12 m, what will the amount of work done?
Ans: Here F = 25 N, s = 12
Then,
∴ W = 25 × 12 = 300 J
Ex: 2) Find the magnitude of force required to displace a cupboard by 20 m from a corner through 600, if the work done is 500 J.
Ans: Here W=500 N, s= 20, θ = 600
Then,
∴ W = F s cosθ
∴ 500 = F × 20 cos60
∴ 500 = F × 20 × 1/2
∴ F = 500/10 = 50 N