Physics Chapter on Energy and Work

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Questions and Answers

What is the formula for calculating potential energy?

  • PE = Fd cos θ
  • PE = mgh (correct)
  • PE = 1/2 mv^2
  • PE = m/g

A ball is thrown vertically upwards. What happens to its potential and kinetic energy as it rises?

  • Potential energy and kinetic energy both increase
  • Potential energy increases, kinetic energy decreases (correct)
  • Potential energy and kinetic energy both decrease
  • Potential energy decreases, kinetic energy increases

What unit of measurement is used for both potential energy and kinetic energy?

  • Joule (J) (correct)
  • Watt (W)
  • Newton (N)
  • Meter (m)

A car traveling at 20 m/s has a kinetic energy of 1000 J. What is its mass?

<p>25 kg (A)</p> Signup and view all the answers

If the work done on an object is 50 J and the displacement is 10 m, what is the force applied in the direction of the displacement?

<p>5 N (C)</p> Signup and view all the answers

What is the potential energy of a 2 kg object that is lifted to a height of 5 m above the ground? (Assume g = 10 m/s²)

<p>100 J (D)</p> Signup and view all the answers

A car is traveling at a constant speed on a flat road. What is the net work done on the car?

<p>Zero work (D)</p> Signup and view all the answers

A ball is thrown horizontally from a cliff. What is the direction of the force of gravity acting on the ball?

<p>Vertical, downwards (A)</p> Signup and view all the answers

Which of the following is NOT a derived quantity?

<p>Mass (D)</p> Signup and view all the answers

What is the work done on a system by a constant force, given the following information: Force = 10 N, angle between the force and the direction of motion = 30 degrees, distance = 5 m?

<p>43.3 J (D)</p> Signup and view all the answers

Which of these is an advantage of the metric system?

<p>It uses simpler relationships for unit conversions. (B)</p> Signup and view all the answers

What is the difference between distance and displacement?

<p>Distance is a scalar while displacement is a vector (A)</p> Signup and view all the answers

What is the displacement of an object moving from point A to point B and then to point C, given that the distance between A and B is 5 m and from B to C is 2.5 m and the object moves in the same direction for all points?

<p>2.5 m (C)</p> Signup and view all the answers

What are the base quantities used to derive the derived quantity 'work'?

<p>Mass, time, distance (D)</p> Signup and view all the answers

Which of the following is NOT a metric prefix?

<p>inch (B)</p> Signup and view all the answers

What is the unit for work in the metric system?

<p>Joule (J) (C)</p> Signup and view all the answers

What is the formula for kinetic energy?

<p>$KE = 1/2mv^2$ (D)</p> Signup and view all the answers

What is the kinetic energy of a shot-put with a mass of 3.8 kg moving at a speed of 20 m/s?

<p>760 J (A)</p> Signup and view all the answers

What is the Work-Energy Theorem?

<p>The total work done on an object is equal to the change in its kinetic energy. (D)</p> Signup and view all the answers

What is the formula for the work done by a non-conservative force?

<p>$Wnc = F.d.cos(theta)$ (A)</p> Signup and view all the answers

What is the formula for the force of friction?

<p>$Ffriction = μ.Fnormal$ (C)</p> Signup and view all the answers

What is the unit of power?

<p>Watts (D)</p> Signup and view all the answers

What is the definition of electric charge?

<p>A fundamental property of subatomic particles that gives rise to the phenomenon of experiencing force in the presence of electric and magnetic fields. (B)</p> Signup and view all the answers

What are the two main types of electric charge?

<p>Positive and negative charges (A)</p> Signup and view all the answers

Which of the following best describes how heat is transferred through radiation?

<p>Heat is transferred through electromagnetic waves. (A)</p> Signup and view all the answers

In the context of the provided text, which of the following is an example of convection?

<p>Heat from a hot air balloon traveling into the atmosphere. (D)</p> Signup and view all the answers

Which of the following scenarios represents an example of conduction?

<p>A metal spoon getting heated when placed in a cup of hot tea. (D)</p> Signup and view all the answers

Which of the following is a key factor that influences the amount of heat produced during an x-ray exposure?

<p>All of the above. (D)</p> Signup and view all the answers

What is the primary reason why excessive heat during an x-ray exposure can be detrimental?

<p>It can cause the x-ray tube to overheat and potentially malfunction. (D)</p> Signup and view all the answers

In the context of x-ray production, what is the 'heat unit' (HU) used to measure?

<p>The amount of heat produced in the x-ray tube during an exposure. (C)</p> Signup and view all the answers

What is the primary function of the cathode in an x-ray tube?

<p>To emit electrons that are accelerated towards the anode. (D)</p> Signup and view all the answers

Which of the following is NOT a form of heat transfer involved in the cooling of an x-ray tube?

<p>Evaporation (C)</p> Signup and view all the answers

What is the unit of electrical charge?

<p>Coulomb (C) (D)</p> Signup and view all the answers

What does the 'additivity of electric charge' principle state?

<p>Charges can be added together algebraically. (D)</p> Signup and view all the answers

What is the charge of a proton?

<p>+1.6 x 10^-19 C (A)</p> Signup and view all the answers

Which of the following statements is TRUE about the 'quantization of electric charge'?

<p>Electric charge can only exist in discrete, indivisible units. (D)</p> Signup and view all the answers

What does Coulomb's Law describe?

<p>The strength of the electrostatic force between two charges. (A)</p> Signup and view all the answers

How does the electrostatic force between two charges change if the distance between them is doubled?

<p>It is reduced to one-fourth. (B)</p> Signup and view all the answers

What is the specific heat capacity of water?

<p>4200 J kg-1 K-1 (C)</p> Signup and view all the answers

Which of the following materials is the best conductor of heat?

<p>Copper (D)</p> Signup and view all the answers

What is the main difference between conduction and convection as methods of heat transfer?

<p>Conduction occurs mainly in solids, convection mainly in fluids. (D)</p> Signup and view all the answers

A piece of metal is heated at one end. How does the heat transfer through the metal?

<p>Molecules at the heated end vibrate faster, transferring energy to neighboring molecules. (D)</p> Signup and view all the answers

Which scenario is an example of convection?

<p>A pot of water boiling on a stove. (D)</p> Signup and view all the answers

How do you explain the process of a convection current?

<p>Hotter fluids become less dense and rise, cooler fluids sink, creating a cycle. (A)</p> Signup and view all the answers

Which of the following substances is the best conductor of heat?

<p>Aluminium (C)</p> Signup and view all the answers

What is the primary reason why sand gets very hot during summer?

<p>Sand is a good conductor of heat and quickly transfers heat from the sun to its surface. (C)</p> Signup and view all the answers

How does radiation differ from conduction and convection?

<p>Radiation does not require a medium to travel, while conduction and convection do. (C)</p> Signup and view all the answers

Flashcards

Work (W)

The energy transferred when a force acts over a distance: W = F.d cos θ.

Potential Energy (PE)

Stored energy due to an object's position, calculated as PE = mgh.

Kinetic Energy (KE)

Energy of a moving object, defined as KE = ½ mv².

Formula for Potential Energy

PE = mass (kg) x gravity (m/s²) x height (m).

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Formula for Kinetic Energy

KE = ½ x mass (kg) x velocity (m/s)².

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Force (F) in Work formula

The influence that can change an object's motion, measured in Newtons (N).

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Gravity (g) value

The acceleration due to gravity is approximately 9.81 m/s² or rounded to 10 m/s².

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Units of Energy

Both potential energy and kinetic energy are measured in Joules (J).

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Derived Quantities

Physical quantities created from base quantities using math operations.

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Metric System Advantages

Simplified conversions based on powers of 10 and universal prefixes.

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Displacement

The change in position of an object, having both magnitude and direction.

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Distance

Total length of the path traveled between two positions.

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Work Equation

Work (W) is the product of force (in direction of motion) and distance: W = F d cosθ.

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Unit of Work

The unit for measuring work is the Joule (J), equivalent to Nm.

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Components of Force

When calculating work, consider the force's direction and distance moved.

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Constant Force

A force that remains the same in magnitude and direction while moving an object.

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Kinetic Energy

Energy an object has due to its motion, calculated as KE = ½ mv².

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Work-Energy Theorem

States that the work done on an object equals the change in its kinetic energy.

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Coefficient of Friction (µ)

A measure of how much frictional force exists between two surfaces in contact.

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Power (P)

The rate at which work is done or energy is transferred, expressed as P = work/time.

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Work Done (W)

The energy transferred when a force acts over a distance, calculated using W = Fd cosθ.

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Electric Charge

A fundamental property of particles that leads to electric force in fields; can be positive or negative.

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Friction Force (Ffriction)

The force resisting the motion of an object; depends on the surface and the normal force.

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Coulomb (C)

The unit of electric charge in the International System.

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Additivity of Electric Charge

When charges combine, their magnitudes add algebraically.

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Conservation of Electric Charge

Electric charge in an isolated system remains constant over time.

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Quantization of Electric Charge

Electric charge exists in discrete units called elementary charges.

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Coulomb’s Law

Describes the force between two point charges based on their magnitudes and separation distance.

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Specific Heat Capacity

Heat required to raise 1 kg of a substance by 1°C or 1 K.

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Formula for Heat Exchange

Q = mcΔT, where Q is heat, m is mass, c is specific heat, and ΔT is temperature change.

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Specific Heat of Water

Water has a specific heat capacity of 4200 J kg-1 K-1.

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Heat Transfer

Exchange of thermal energy between physical objects.

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Thermal Equilibrium

When all involved objects reach the same temperature.

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Conduction

Heat transfer within a substance, molecule by molecule.

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Convection

Heat transfer by the mass movement of a fluid.

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Radiation

Transfer of energy through electromagnetic waves.

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Convection Current

Cycle of rising hot fluid and sinking cooler fluid.

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Good Conductors

Materials that transfer heat easily, e.g., metals.

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Poor Conductors (Insulators)

Materials that do not transfer heat well.

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Electromagnetic Waves

Waves made of electric and magnetic fields that carry energy through space.

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X-ray Production

When electrons collide in a vacuum tube, most kinetic energy turns to heat, with less than 1% yielding x-radiation.

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Heat Unit (HU)

A measure of heat produced during x-ray exposure, calculated as HU = kVp x mA x time(s).

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Cooling Methods

The three methods used to cool an x-ray tube: radiation, conduction, and convection.

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Conversion to Thermal Energy

More than 99% of the kinetic energy of electrons is converted into heat in an x-ray tube.

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Alpha Particles

Helium nuclei released during the radioactive decay of Uranium-238 into Thorium-234.

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Study Notes

Course Information

  • Course Title: Fundamental Physics for Radiographers
  • Course Code: RXD12402
  • Instructor: Izza Nadia binti Mohd Maulana
  • Senior Lecturer

Subtopics

  • Introduction to Physics
  • Work, Energy, and Power
  • Properties of Electrical Charges
  • Law of Conservation of Energy
  • Heat and Temperature
  • Heat Transfer
  • Heat Energy in X-ray Tube

Learning Outcomes

  • Describe work, energy (potential and kinetic), and power
  • Describe the law of conservation of energy
  • Describe electrical charges and Coulomb's Law
  • Describe heat and temperature
  • Describe heat transfer processes (conduction, convection, radiation)

Introduction to Physics

  • Physics studies interactions of energy, matter, space, and time
  • Aims to describe the function of everything around us, from tiny charged particles to large objects
  • Phenomena can be accurately described by the laws of physics

Physical Quantities and Units

  • Quantities are defined by how they are measured or calculated from other measurements
  • Use standardized units for meaningful comparison

Base Quantities

  • Length (meter, m)
  • Mass (kilogram, kg)
  • Time (second, s)
  • Temperature (Kelvin, K)
  • Current (Ampere, A)

Derived Quantities

  • Derived from combinations of base quantities (multiplication or division)
  • Examples include area (m²), volume (m³), density (kg/m³), speed (m/s), acceleration (m/s²), work (Joule, J), and power (Watt, W)

Metric Prefixes

  • Conversions in metric systems use powers of 10
  • Simplifies conversions compared to non-metric systems (e.g., US customary units)

Displacement vs. Distance

  • Displacement: change in position, includes direction and magnitude
  • Distance: magnitude of displacement between two positions, total length of path traveled

Work

  • Work done by a constant force = component of force in motion direction multiplied by distance
  • Formula: W = Fd cos θ
  • Unit: Joule (J) = Nm

Energy in Kinematics

  • Kinematics: study of motion of mechanical bodies and systems
  • Two types of energy:
    • Potential energy
    • Kinetic energy

Potential Energy

  • Energy stored due to an object's position
  • Formula: PE = mgh
  • Where: m = mass, g = gravity, h = height
  • Unit: Joule (J)

Kinetic Energy

  • Energy of motion
  • Formula: KE = 1/2 mv²
  • Where: m = mass, v = velocity
  • Unit: Joule (J)

Conservation of Energy

  • Energy can change forms but cannot be created or destroyed
  • In a closed system, the sum of kinetic and potential energy remains constant
  • Total energy remains constant but can change between different forms

Heat Transfer

  • Heat: energy from hotter to colder region
  • Temperature: degree of hotness/coldness
  • Three methods:
    • Conduction
    • Convection
    • Radiation

Conduction

  • Heat transfer by direct contact
  • Vibrating molecules at one end transfer energy to adjacent molecules

Convection

  • Heat transfer by mass movement of fluid (liquids or gases)
  • Warmer fluid rises, cooler fluid descends, creating currents

Radiation

  • Heat transfer via electromagnetic waves
  • Examples: from the microwave, the sun

Heat Energy in X-Ray Tube

  • Cathode emits electrons, anode collects them
  • Most of kinetic energy converted to heat
  • Cooling methods:
    • Radiation
    • Conduction
    • Convection
    • Oil cooling
  • Heat Unit (HU): kVp x mA x time (s)

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