# For a particle in one dimensional motion, which of the following is true?

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For a particle in one dimensional motion, which of the following is true?

(a) Zero speed at any instant may have zero acceleration at the instant

(b) Zero speed may have non-zero velocity

(c) Constant speed must have zero acceleration

(d) Positive value of acceleration must be speeding up

This question was posed to me by my college director while I was bunking the class.

This key question is from Acceleration due to Gravity topic in section Laws of Motion of Engineering Physics I

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Correct choice is (c) Constant speed must have zero acceleration

Explanation: When a particle moves with a constant speed in the same direction, neither the magnitude nor the direction of velocity changes and so acceleration is zero. In case a particle rebounds instantly with the same speed, its acceleration will be infinite which is physically not possible.

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