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Q2.1: MOTION IN A STRAIGHT LINE Solutions — NCERT Physics - Part 1
⚠️ Common Exam Traps & Conceptual Pitfalls
Students frequently judge an object as a point by comparing its size to the total travel distance, overlooking that the relevant length scale is the curvature or displacement over which the object's orientation changes; when the object's dimension is comparable to that radius of curvature (as in a spinning ball or tumbling beaker), the point‑mass approximation breaks down.
In which of the following examples of motion, can the body be considered approximately a point object: (a) a railway carriage moving without jerks between two stations. (b) a monkey sitting on top of a man cycling smoothly on a circular track. (c) a spinning cricket ball that turns sharply on hitting the ground. (d) a tumbling beaker that has slipped off the edge of a table.
Step-by-Step Verified Solution
**Answer:** (a) Yes, (b) Yes, (c) No, (d) No.
**Step-by-Step Explanation:**
(a) The size of the carriage is very small compared to the distance between two stations, so it can be treated as a point object.
(b) The size of the monkey is very small compared to the size of the circular track, so it can be considered as a point object.
(c) The size of the spinning cricket ball is comparable to the distance through which it turns sharply on hitting the ground, so it cannot be considered as a point object.
(d) The size of the beaker is comparable to the height of the table from which it slipped, so it cannot be considered as a point object. [citation:6]
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