Answer:
(a) True. When a body begins to fall freely under gravity, its speed is zero but it has non-zero acceleration of .
(b) False. Speed is the magnitude of velocity and the magnitude of non-zero velocity cannot be zero.
(c) True. 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.
(d) False. If the initial velocity of a body is negative, then even in case of positive acceleration, the body speeds down. A body speeds up when the acceleration acts in the direction of motion.
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