The object starts to fall from rest, which means the speed changes from 0 to some positive number. But I don’t understand why acceleration decreases? Isn’t the acceleration of free fall 9,81? So an object at rest that experiences free fall will eventually gain an acceleration of 9,81 m/s^2. I chose C.
Answer credited to @Asafmen
You got it confused due to 2 reasons:
When you free fall, there are 3 stages possible:
- The upward phase, in which you gain acceleration.
- The stop phase, when acceleration is 0, can either occur as a stop in a pick point (the moment you or the object stop going up but yet to go down).
- The decreasing acceleration due to Air Friction which is not neglected in this question.
When you skydive, you go through phases 2&3. You also reach terminal velocity in which acceleration is 0 and speed is constant.
The speed will increase, but the initial acceleration will be 9.8 {\frac{m}{s^2}} and will decrease (even though very little) due to Air Friction.
Acceleration during free falls is either constant or decreasing, and the only way for it to increase is by a non-gravitational force that will drive the object outwards.