Kinetic Energy MCQs Quiz | Class 9
Welcome to the Class IX Science (Code 086) quiz on Unit III: Motion, Force and Work. This quiz specifically covers Kinetic Energy, focusing on its meaning, definition, and dependence on mass and speed. Test your understanding of how energy of motion works in physics. Click ‘Submit Quiz’ to check your score and download the detailed Answer PDF for revision.
Understanding Kinetic Energy
Kinetic Energy (KE) is the energy possessed by an object due to its motion. Any object that is moving has kinetic energy. It is a scalar quantity, meaning it has magnitude but no specific direction. The standard unit for measuring kinetic energy is the Joule (J).
Formula and Factors
The kinetic energy of an object of mass ‘m’ moving with a uniform velocity ‘v’ is given by the expression:
KE = 0.5 x m x v^2 (half of mass times velocity squared)
- Mass (m): Kinetic energy is directly proportional to mass. If you double the mass, the kinetic energy doubles.
- Velocity (v): Kinetic energy is directly proportional to the square of the velocity. If you double the velocity, the kinetic energy increases by four times.
Work-Energy Relationship
The work done on an object to change its velocity is equal to the change in its kinetic energy. For an object starting from rest, the work done to bring it to a velocity ‘v’ is equal to the kinetic energy it acquires.
| Factor | Effect on Kinetic Energy |
|---|---|
| Double the Mass | Becomes 2 times |
| Double the Velocity | Becomes 4 times |
| Halve the Velocity | Becomes 1/4 times |
Key Takeaways
- An object at rest has zero kinetic energy.
- A heavy truck moving at the same speed as a small car has more kinetic energy.
- Stopping a fast-moving object requires more work than stopping a slow-moving one.
Extra Practice Questions
- A ball of mass 2 kg moves at 3 m/s. Calculate its KE. (Answer: 9 J)
- If the velocity of a car becomes 3 times, how does KE change? (Answer: 9 times)
- What is the commercial unit of energy? (Answer: Kilowatt-hour)
- Is kinetic energy ever negative? (Answer: No, because mass and v-squared are positive)
- Does a compressed spring have kinetic energy? (Answer: No, it has potential energy)
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