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Work Done

Last Updated : 23 Jul, 2025
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Every day, we are involved in countless activities—from lifting a school bag, climbing stairs, or opening a door to pushing a swing in the park. While these tasks may seem different, they all have something in common: they require effort. But what exactly makes something happen when we apply effort? The answer lies in the concept of force and how it brings about movement.

Work is done only when a force moves an object. So, actions like pushing a cart or kicking a ball involve scientific work, but if there is no movement, no work is done.

Work Done

Work Done in Physics

Work is a physical quantity that occurs when a force causes an object to move or be displaced. The amount of work done is calculated as the product of the force applied and the displacement of the object in the direction of the force. According to physics, if there is no displacement, no work is done—regardless of how much force is applied.

Work done by the weight lifter


This above image illustrates the concept of work done in physics. It shows a man lifting a weight of 200 Newtons vertically upward to a height of 2 meters.

In physics, work is said to be done when a force is applied to an object and the object moves in the direction of that force. In this case, the man applies an upward force to lift the weight, and the weight moves upward as a result.

This gives us the idea of following conditions necessary for work done

  • Force must be applied.
  • There must be some amount of displacement.

Hence, according to the definition in physics, work is done only when an object is moved or lifted by an applied force. Although force and displacement are vector quantities, work has no direction, making it a scalar quantity.

Work can vary depending on the context. For instance, when compressing a gas at constant temperature, the work done is the product of pressure and volume change. Work transfers energy to an object, so the amount of work done is directly related to the increase in the object's energy.

If the applied force acts opposite to the direction of motion, the work done is negative, indicating that energy is being taken away from the object.

The Science Behind 'No Work Done' Despite Effort!

Consider the following scenario,

Imagine a waiter carrying a tray high above his head with one arm while walking steadily across a room. At first glance, it seems like he's doing a lot of work—after all, holding and balancing a tray while walking takes effort.

However, in physics, the definition of work is different. Work is only done when a force causes an object to move in the direction of that force.

In this case, the waiter applies an upward force to support the tray, but the tray is moving horizontally as he walks. Since the direction of the force (upward) is not the same as the direction of movement (forward), no work is done on the tray in the scientific sense.

Formula for Work Done ,

The product of the magnitude of applied force and the distance travelled by the body equals the total work done by this force.

The formula for scientifically completed work will be as follows:

W = F·d

The force acting on the block is constant in this example, but the direction of the force and the direction of displacement impacted by it are not. Force F reacts at an angle θ to the displacement d in this case.

W=∣F∣⋅∣d∣⋅cosθ

where,
W is the work done by the force.
F is the force,
θ is the angle between the force vector and the displacement vector,
d is the displacement caused by the force.

Derivation for the Work Done Formula

From Newton’s second law:

F=m⋅a

Use kinematic equation:

v^2 = u^2 + 2as ⇒as=\frac{v^2 - u^2}{2}

Multiply both sides by 'm'

mas = \frac{1}{2}mv^2 - \frac{1}{2}mu^2

But F=ma, and work done W=F⋅s, so:

W=F⋅s=mas

Unit of Work

  • SI unit of work done is Joule(J).
  • Other unit of work done is Newton meter(Nm)

Dimension of Work Done

The dimension of work done is [ML2T–2]. It is defined as the product of the magnitude of displacement d and the component of the force acting in the displacement direction.

Types of Work Done

On the basis of the angle between the force and the displacement work done can be categorized into three types,

  1. Positive Work
  2. Negative Work
  3. Zero Work

1. Positive Work

When a force moves an item in a the direction of force, the work done is considered positive. The motion of a ball falling towards the earth, with the displacement of the ball in the direction of gravity, is an example of this sort of labour.

When force is applied to an item at an angle 0 ≤ θ < 90°, it is said to be positive work done.

2. Negative Work

When force and displacement are in opposite directions, it is considered that the work is negative. For example, if a ball is thrown upwards, the displacement will be upwards; nevertheless, the force due to gravity will be downwards.

When force is applied to an item at an angle of 90° ≤ θ ≤ 180°, it is said to be negative work done.

3. Zero Work Done

The total work done by the force on the item is 0 in the following two cases

Case 1: If the displacement caused by the force is zero. For example, if you push a wall the displacement of wall is zero hence work done is zero

Case 2: If the direction of the force and the displacement are perpendicular to each other. For example if you carry a load on your head and walk straight then the force applied by you in carrying the load is upward and your direction of movement is forward then the angle between force and displacement here is zero.

Work Done by a Constant Force

When a force acts on an item over a long distance, the thing undergoes work. Physically, the work done on an item is the change in energy that the object possesses.

Thus, we can define the work done as the change in the energy of the object(either kinetic or potential). The total energy of the system is always constant and it can be converted to other forms using the work done.

Work Done by the System

When we talk about work, we focus on the impact that the system has on its surroundings. As a result, we consider work to be positive when the system makes an attempt to improve the environment (i.e., energy leaves the system). If work is done on the system, the work is negative (i.e., energy added to the system).

Examples of the work done by the system are,

  • The output shaft of a turbine rotating a generator
  • A rocket propelling itself upward by expelling gas
  • An internal combustion engine powering a vehicle
  • A pump pushing water through a pipeline

Factors Affecting Work Done

Various factors affect the work done by an object which are,

  • Force applied
  • Displacement
  • Angle Between Force Vector and Displacement Vector

Let's look at some of the factors that affect the work done by an object.

Force Applied

It is described as a push or a pull that may cause any massed object's velocity and acceleration to alter.

The amount and direction of force are both vector quantities. If the force acting on an item is zero, regardless of whether the object is in a dynamic or static state, the force does not work.

Displacement

It is a vector quantity that represents the smallest distance between an object's starting and final positions. The net work done by a force acting on an item is zero if the resultant displacement in the direction of force is zero.

For example, if we push a hard wall with all our might but still fail to move it, we might say we have done no work on the wall.

Angle Between Force Vector and Displacement Vector

The work done by a force depends on the direction of displacement relative to the force. If the displacement is in the same direction as the force, the work is positive. If it is in the opposite direction, the work is negative, like friction acting against a moving object.

When the displacement is perpendicular to the direction of the applied force, the work done is zero. For example, in circular motion, the force is toward the center, but the object moves along the path—so no work is done.

Relation between Work and Energy

Work and energy are closely related concepts in physics. Their relationship can be understood through the following key points:

  • Energy is defined as the ability to do work.
  • Work is defined as the transfer of energy from one object or form to another.
  • When an object gains or loses energy, it’s due to work being done.

Work-Energy Theorem:

W = \Delta E = E_{\text{final}} - E_{\text{initial}}

Hence,

Work = Change in Energy = Energy Transferred

Rate of Work Done

The rate at which work is done or energy is transferred per unit time is called Power.

The physical quantity that measures the rate of work done is called Power.

It is given by the formula,

P = W/t

Solved Examples on Work Done

Example 1: The rope pulls the box along the floor, creating a 30° angle with the horizontal surface. The box is dragged for 20 meters, with a force of 90 N applied by the rope. Where can I find the force's final work?

Solution:

Here,
The angle between force and displacement, θ = 30°
The displacement of the box, d = 20 m
The force applied on the box, F = 90 N
So, total work done by the force is,
W = F .d cosθ = 90 × 20 × 0.866 J
= 1558.8 J ≈ 1560 J
Hence, the work done by the force is 1560 J.

Example 2: With Force 10 N engaged at an angle of 60° from the horizontal, a girl thrusts a toy car from the stationary state on the horizontal floor. The toy car weighs 4 kg. In 10 seconds, can you find the girl's work?

Solution:

Initially, we can resolve the force into two components such as horizontal and vertical component;
Horizontal component = 10 cos60° = 5 N
Vertical component = 10 sin60° = 8.66 N
Now we need to figure out how much work we've done and how far we've travelled.
Horizontal force will now be the sole source of acceleration for that toy cart.
Acceleration, a = F/m = 5 N /4 kg = 1.25 m/s²
We can obtain displacement from the formula:
s = u t + 1/2 a t² = 0 + 0.5 × 1.25 × 10² m = 62.5 m
So, the work done will be:
W = F × s 
    = 5 × 62.5 J
    = 312.5 J
Hence, the work done by the car is 312.5 J

Example 3: Calculate the Work Done on the Body when a force pg 50 N displaces it by 5m

Solution: 

Formula for the work done is,
W = F × d
Given,
F = 50 N
d = 5m
Substituting these values in the above formula we get
W = 50 × 5
W = 250 Joule
Thus, the work done on the body is 250 J.

Example 4: A Box is pulled over an inclined plane with a force of 5 KN. If the displacement of the box is 5 m and the inclination of the plane is 30°. Find the work done (neglecting the weight of the box and friction between the plane and the box)

Solution:

Force applied on the box is 5 KN = 5000 N.
As the box is placed on an inclined plane with an angle of 30° the two components of the forces are, F cos 30° and F sin 30°.
The force which displace the body is F cos 30°= 5000 × (√3 / 2)

      = 2500√3

Displacement of the box is 5 m.
Work done is given by the formula,
W = F × d
  = 2500√3 × 5 
  = 12500√3 Joule
Thus, the work done is 12500√3 J

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