7)an object is thrown straight up with an initial velocity of 3 m/s. what is its acceleration at its maximum height? a)zero b)3 m/s2 c)-9.8 m/s2 d)none of the above

C.
It is a motion with uniform acceleration, meaning that the acceleration will not change.
The object is thrown upwards with a positive velocity. This shows that the upward direction is positive. The object will decelerate due to gravity at a magnitude of 9.81 m/s2. Therefore, the acceleration is -9.81 m/s2.
Note that even though the velocity of the object is momentarily 0 m/s at maximum height, there is still a constant acceleration.
This allows the object first decelerate upwards, then change direction at max height, and finally accelerate downwards. So in this case, the acceleration is always negative and unchanged.

Bag of bolts weight 29.4n