Scientific Conception of Work – Long Answer Questions

Medium Level (Application & Explanation)

Answer:

In physics, work is done when a force causes a displacement in the same or partly same direction.
Two conditions: a force must act, and a displacement must occur.
If you push a wall and it does not move, there is force but no displacement. So, no work is done.
If a book falls, gravity is the force and there is downward displacement. So, work by gravity is done.
When you lift a book, your force is upward and the book moves upward. So, positive work is done by you.
Thus, both force and displacement are essential to say that work is done.

Answer:

Positive work: Force and displacement are in the same direction. Example: lifting a book upward. Your force is up; displacement is up.
Negative work: Force and displacement are in opposite directions. Example: lowering a load slowly. Your force is up; displacement is down.
Zero work: Force is perpendicular to displacement or there is no displacement.
Example of zero work (perpendicular): carrying a bag horizontally. Your upward force supports weight; movement is horizontal.
Example of zero work (no displacement): pushing a locked door that does not move.
These ideas show that direction matters in deciding work.

Answer:

Riding a bicycle: You do work against friction and air resistance as the cycle moves forward. There is force and displacement.
Carrying groceries at constant height on level ground: Your vertical force supports weight, but motion is horizontal. So, work on the bag is zero by you.
If you lift the groceries to pick them up, you do positive work.
Sitting on a chair: You apply force on the chair and the chair on you, but there is no displacement. So, no work is done.
Your body may feel tired, but that is physiological effort, not mechanical work on the object.
Physics focuses on force with displacement to define work.

Answer:

In physics, every displacement is due to some force. It can be a contact force or a non-contact force.
A falling object moves because of gravity. Gravity is a force. So, work is done by gravity on the object.
You may not be actively pushing the object. But a force still acts.
The confusion comes from mixing “no applied force by you” with “no force at all.”
In free fall, gravity does positive work as the object speeds up downward.
Thus, “displacement without force” is not correct in physics. Some force must cause the motion.

Answer:

Work needs both force and displacement.
If you push a sled hard and it does not move, you feel tired, but no work is done on the sled.
The displacement is zero, so the work on the sled is zero.
Your body still uses energy internally. That is physiological work, not mechanical work on the sled.
Physics measures work on the object based on its movement due to the applied force.
So, applying force alone does not guarantee work in the scientific sense.

Answer:

The person’s force on the box is upward to balance gravity.
The box’s displacement is horizontal while walking.
Force and displacement are perpendicular. So, work done by the person on the box is zero.
If the person lifts the box upward, then positive work is done during lifting.
While just carrying at constant height and speed, work on the box is not done by the person.
The person may feel tired, but that is not mechanical work on the box.

Answer:

Her pull can be split into two parts: horizontal and vertical components.
The trolley’s displacement is horizontal.
Only the horizontal component of the pull does work on the trolley.
The vertical component does no work if the trolley does not move up or down.
At constant speed, net work on the trolley is zero (no change in kinetic energy).
Work done by her pull is balanced by negative work done by friction/air resistance.

Answer:

When the book is held at rest, there is no displacement. So, work by your hand on the book is zero.
When you lower it slowly, the displacement is downward.
Gravity acts downward, so gravity does positive work during lowering.
Your hand’s force acts upward while displacement is downward, so your hand does negative work.
The book’s loss of potential energy is partly transferred as work and may appear as heat in your muscles and surroundings.
This shows how direction decides the sign of work.

Answer:

The bird’s wings push air and do positive work to keep moving.
Gravity pulls downward and does negative work.
Air resistance also does negative work (opposes motion).
Since the speed is constant, the net work on the bird is zero (no change in kinetic energy).
Positive work by the wings equals the total negative work by gravity and drag.
The bird uses internal energy (food) to supply this work.

Answer:

The car has no displacement as it is not moving.
So, the work done on the car by external forces is zero.
The engine burns fuel and produces energy, but without movement, it does no mechanical work on the car’s motion.
The energy is mostly lost as heat, sound, and vibration.
Parts like the engine and exhaust become hot due to this energy conversion.
Hence, energy is used, but no work is done on the car in the physics sense.