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Q2.7: NCERT Physics - Part 1 MOTION IN A STRAIGHT LINE 2.7 Solution: Read each statement below carefully and state with reasons and…
⚠️ Common Exam Traps & Conceptual Pitfalls
Students often think that a zero speed can coexist with a non‑zero velocity, forgetting that velocity is a vector and its magnitude equals speed. Likewise, a positive acceleration does not automatically mean the particle is speeding up; it only increases speed when it points in the same direction as the velocity ($a>0$ speeds up only if $v>0$, but if $v<0$ it slows down).
Read each statement below carefully and state with reasons and examples, if it is true or false; A particle in one-dimensional motion (a) with zero speed at an instant may have non-zero acceleration at that instant (b) with zero speed may have non-zero velocity, (c) with constant speed must have zero acceleration, (d) with positive value of acceleration must be speeding up.
Step-by-Step Verified Solution
**Answer:** (a) True, (b) False, (c) False, (d) False.
**Step-by-Step Explanation:**
(a) True. At the highest point of a ball thrown upward, speed is zero but acceleration is 9.8 m/s_ downward.
(b) False. If speed is zero, velocity magnitude is zero, so velocity is zero.
(c) False. Constant speed with changing direction implies non-zero acceleration (e.g., uniform circular motion).
(d) False. Positive acceleration may be slowing down if velocity is negative (e.g., a ball moving upward with downward acceleration).
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