A particle in one-dimensional motion. Choose the correct
(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 & explanation
Correct answer: option 1
(a) when an object is thrown vertically up in the air, its speed becomes zero at maximum height. However, it has acceleration equal to the acceleration due to gravity so (a) is true.
(b) Speed is the magnitude of velocity. When speed is zero, the magnitude of velocity along is zero, it may have directional sense. Hence (b) is false.
(c) Speed is the magnitude of velocity. Constant speed does not imply constant velocity as direction change may happen. For example in uniform circular motion of a particle its acceleration is not zero. This statement is false.
(d) in a situation where acceleration is positive and velocity is negative at the instant then, for all the time before velocity becomes zero, there is slowing down of the particle. Such a case happens when a particle is projected upwards.
this statement is false.