Final answer:
The acceleration due to gravity is always directed downwards when a ball is thrown upwards, both when the ball is rising and when it is falling. The graph of the ball's vertical acceleration over time shows a constant negative value.
Step-by-step explanation:
The statement that 'As the ball rises, its acceleration is upwards; as it falls, its acceleration is downwards' is false. In physics, when a ball is thrown upwards, it is affected by gravity all through its motion. Consequently, the acceleration due to gravity is always directed downwards, toward the center of the Earth. This is true regardless of whether the ball is rising, at its peak, or falling back down. Therefore, the correct answers to the questions are:
- (2) A negative value that does not change with time (This represents the constant acceleration due to gravity.)
- (8) False (When a rock is thrown into the air, the increase in height increases its potential energy, not kinetic energy. Conversely, as it falls and gains speed, its kinetic energy increases, not potential energy.)
- (21) (a) The ball's velocity is zero at its peak. (b) Yes, its velocity changes direction at the peak. (c) The acceleration due to gravity has the same sign on the way up and on the way down; it is always downward.
- (18) False (The position vs time graph of an object that is speeding up is not necessarily a straight line; it depends on the type of motion.)
The graph of the ball's vertical acceleration versus time would show a constant negative value, representing the constant effect of gravity. The graph of the ball's horizontal velocity would be constant since no forces are acting in the horizontal direction once it leaves the hand, assuming air resistance is negligible.