Class 9 Science: Work and Energy Key Highlights

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Questions and Answers

What is the SI unit of energy or work?

  • Newton
  • Joule (Nm) or Kgm2s−2 (correct)
  • Pascal
  • Watt

What is the definition of work done on an object?

  • The product of mass and acceleration
  • The product of the force and the angle between the force vector and displacement vector
  • The product of the magnitude of the force acting on the body and the displacement in the direction of the force (correct)
  • The product of the magnitude of the force acting on the body and the total displacement

What is mechanical energy composed of?

  • Chemical energy and electrical energy
  • Kinetic energy and potential energy (correct)
  • Potential energy and heat energy
  • Heat energy and light energy

What is kinetic energy defined as?

<p>$\frac{1}{2}mv^2$ where m is mass and v is velocity (A)</p> Signup and view all the answers

When two identical bodies are in motion, which body has more kinetic energy?

<p>The body with a higher velocity (A)</p> Signup and view all the answers

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Study Notes

Energy and Work

  • The SI unit of energy and work is the joule (J).

Work Done on an Object

  • Work done on an object is defined as the product of the force applied to the object and the distance over which that force is applied, measured in the direction of the force.
  • Mathematically, work (W) is expressed as W = F × d × cos(θ), where F is the force, d is the distance, and θ is the angle between the force and the direction of motion.

Mechanical Energy

  • Mechanical energy consists of two main components: potential energy and kinetic energy.
  • Potential energy is the stored energy based on an object's position or configuration, while kinetic energy is energy associated with motion.

Kinetic Energy

  • Kinetic energy is defined as the energy that an object possesses due to its motion, calculated using the formula KE = 0.5 × m × v², where m is mass and v is velocity.

Identical Bodies in Motion

  • When two identical bodies are in motion, the body with the higher speed has more kinetic energy, since kinetic energy is directly proportional to the square of the velocity.

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