Verified Solution • 2025–26 Session
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Q5.17: NCERT Physics - Part 1 WORK, ENERGY AND POWER 5.17 Solution: The bob A of a pendulum released from 30� to the vertical hits…
⚠️ Common Exam Traps & Conceptual Pitfalls
Students often incorrectly assume both bobs continue moving or that the striking bob rebounds, failing to recognize that in a 1D elastic collision between equal masses where one is initially at rest, the velocities are completely exchanged. Consequently, the striking bob stops dead at the mean position, and the target bob moves off with the initial velocity.
The bob A of a pendulum released from 30� to the vertical hits another bob B of the same mass at rest on a table as shown in Fig. 5.15. How high does the bob A rise after the collision? Neglect the size of the bobs and assume the collision to be elastic.
Step-by-Step Verified Solution
**Answer:** Bob A comes to rest and bob B rises to the same height.
**Step-by-Step Explanation:**
For an elastic collision between equal masses, the velocities are exchanged. Since bob B is initially at rest, after collision bob A stops and bob B moves with the velocity of A.
Bob B will rise to the same height from which A was released (30� position). Bob A remains at the mean position.
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