Question

when is the acceleration of body negative

Answer 1

it is negative when the object is in motion and the body tries to stop it and make final velocity zero

Answer 2

The acceleration of body is said to be negative when the acceleration is taking place in the opposite direction of the motion of the body. It tends to decrease the speed of body and bring it to rest. For ex-when brakes are applied to a vehicle then the vehicle undergoes negative acceleration.