## College Physics (4th Edition)

The correct answer is: $A. 4.5~s$
We can find the time it takes the rock to fall $100~m$: $y = \frac{1}{2}at^2$ $t = \sqrt{\frac{2y}{a}}$ $t = \sqrt{\frac{(2)(100~m)}{10~m/s^2}}$ $t = 4.5~s$ The correct answer is: $A. 4.5~s$