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QPage 12: Q1: HC Verma: Concepts of Physics - Volume 2 Heat and Temperature Page 12: Q1 Solution: A spinning wheel is brought in contact with an identical wheel…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often assume that friction simply "drains" every energy of the spinning wheel, so they mark internal and total energy as decreasing. In reality friction converts the wheel's kinetic (mechanical) energy into internal (thermal) energy, raising the wheel’s internal energy while the sum of kinetic + internal (the wheel’s total energy, neglecting external losses) stays constant. Recognize the direction of energy flow to avoid marking internal or total energy as decreasing.

A spinning wheel is brought in contact with an identical wheel spinning at identical speed. The wheels slow down under the action of friction. Which of the following energies of the first wheel decreases?

Multiple Choice Options

  • A a) Kinetic
  • B b) Total
  • C c) Mechanical
  • D d) Internal

Step-by-Step Verified Solution

**Answer:** a), b), c), d) all decrease. **Step-by-Step Explanation:** When a spinning wheel is brought in contact with an identical wheel, friction slows it down. Its kinetic energy decreases. Total energy (which includes rest mass energy) remains constant in a closed system, but the mechanical energy and internal energy distribution changes. The kinetic energy, mechanical energy decrease. The internal energy of the first wheel increases due to friction, but the question asks which of its energies decreases. All of a), b), c) decrease (for the first wheel).

All Questions in this Chapter

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