Question

13. (1) When do you say that an object has positive acceleration?
(ii) When do you say that an object has negative acceleration?
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Answer 1

When a car is starting then it's acceleration is positive but when that is stopping then his acceleration is negative

Answer 2

positive acceleration occurs due to the increase in speed
when the velocity of a body decreases with respect to time that is final velocity is smaller than the initial velocity then this can called as negative acceleration