Question

An object of 4.50 kg fell for a total of 3.40 seconds before hitting the ground. If the initial velocity of the object was zero, from what height did it fall? (Ignore air resistance)

Answer 1

Equation of motion of an object is $y(t) = h - \frac{g t^2}{2}$, where $h$ is the initial height. After time $t = 3.4 s$ $y(t)$ is zero, hence: $0 = h - \frac{g t^2}{2}$, from where $h = \frac{g t^2}{2} \approx 56.7 m$.