Kevin S. Huang

2007: Problem 4

Topic: Kinematics
Concepts: Free fall

Solution:

Recall one of our kinematics equations for uniform acceleration:

x=v_0t+\frac{1}{2}at^2

For dropping an object from rest, we have $v_0=0$ and $a=g$ :

d=\frac{1}{2}gt^2

In the first unit of time,

h=\frac{1}{2}gt_0^2

In the total two units of time,

h’=\frac{1}{2}g(2t_0)^2

Hence, the object fell

h’-h=\frac{1}{2}g(2t_0)^2-\frac{1}{2}gt_0^2=3\left(\frac{1}{2}gt_0^2\right)=3h

during the second unit of time so the answer is C.