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QPage 47: Q10: HC Verma: Concepts of Physics - Volume 2 Calorimetry Page 47: Q10 Solution: A bullet of mass 20 g enters into a fixed wooden block with a…

⚠️ Common Exam Traps & Conceptual Pitfalls

When computing kinetic energy, always express mass in kilograms and speed in meters per second. Using grams directly in $KE= frac12mv^2$ inflates the result by a factor of 1000, leading to a wildly incorrect internal‑energy change.

A bullet of mass 20 g enters into a fixed wooden block with a speed of 40 m s−140 \text{ m s}^{-1} and stops in it. Find the change in internal energy during the process.

Step-by-Step Verified Solution

**Answer:** The change in internal energy is 16 J. **Step-by-Step Explanation:** Given: Mass of bullet = 20 g = 0.02 kg; Speed = 40 m/s. Initial kinetic energy:
KE=12×0.02×402=16 JKE = \frac{1}{2} \times 0.02 \times 40^2 = 16 \text{ J}
Since the bullet stops, all kinetic energy is converted into internal energy. Change in internal energy = 16 J.[citation:2]

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