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PART - 1 CH - 2 Motion in a Straight Line — Physics STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 SciencePhysicsPART - 1 CH - 2 Motion in a Straight Line4 Marks
Question
Read the 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.
✓

Answer

(a) The statement is true, because if the motion of the ball is upward then its speed at the highest point will be zero but the value of acceleration in the downward direction will be $9.8 m / s ^2$ which is equal to the acceleration due to gravity, which acts downwards. Will keep doing.
(b) The statement is false. Because speed is the magnitude of velocity. When speed is zero, the magnitude of velocity will be zero, hence the value of velocity will be zero.
(c) True, when a particle is moving in a straight line with the same speed, then its velocity remains constant with time. Therefore,
Acceleration will be $=\frac{\text { Change in velocity }}{t}=$ Zero
Example : Collision of an elastic object with an elastic plane.
(d) False, because if we consider the vertical downward direction of gravitational acceleration to be positive then the speed of a ball thrown vertically upwards will slow down, but the statement can also be true if the direction of motion itself is considered to be the positive direction of acceleration. Let it be taken.

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