An object's distance $s$ after time $t$ can be written as $s = \frac{1}{2}at^2$, where $a$ is its acceleration. State two conditions that must be true for this formula to describe the object's motion.
A student photographs a steel ball of radius $5.0\,\text{cm}$ as it drops from rest. As shown in Fig. 2.1, the ball’s image is blurred. The blur occurs because the ball is moving while the photograph is being taken.
Calculate, to an appropriate number of significant figures, how long the ball has been falling before the photograph is taken.
Calculate, to an appropriate number of significant figures, the duration for which the photograph is taken.
In (b), the student takes a second photograph starting at the same point on the scale. The ball has the same radius but is less dense, so air resistance is not negligible. State and explain the changes that will appear in the photograph.