Question

(1)when do you say that an object has positive acceleration?
(2) when do you say that an object has negative acceleration?

Answer 1

Positive acceleration=​ A bus or car moving with increasing speed has positive acceleration. We can say that it is accelerating with the direction of travel.
Negative acceleration=​In the above example, if we apply the break, the speed of the car decreases. Then it has negative acceleration.

Answer 2

if a velocity of a body is increasing ,then a body has positive acceleration .
and
if the velocity of a body decrease, then a body has a negative acceleration