Answer
For an object starting at rest, the distance fallen in 1 second is 5 m. After 4 seconds, it will have fallen a distance of 80 m.
Work Step by Step
This is discussed on page 48.
$$d_{1}=\frac{1}{2}gt^{2}=\frac{1}{2}\times10m/s^{2}\times(1 s)^{2}=5 m$$
$$d_{2}=\frac{1}{2}gt^{2}=\frac{1}{2}\times10m/s^{2}\times(4 s)^{2}=80 m$$
