Question

A body is dropped from a height of 320m. The acceleration due to gravity is 10m/s^2?
(a) How long does it take to reach the ground?
(b) What is the velocity with which it will strike the ground?

Answer 1

Given,
$$\begin{gathered} \mathrm{h}=320\mathrm{m} \\ \mathrm{g}=10\mathrm{m}/{\mathrm{s}}^2 \\ \mathrm{u}=0 \\ \mathrm{Using},{\mathrm{v}}^2-{\mathrm{u}}^2=2\mathrm{gh} \\ \mathrm{or}{\mathrm{v}}^2-0=2\times 10\times 320=6400 \\ \mathrm{or}\mathrm{v}=80\mathrm{m}/\mathrm{s} \\ \mathrm{This}\mathrm{is}\mathrm{the}\mathrm{velocity}\mathrm{with}\mathrm{which}\mathrm{the}\mathrm{body}\mathrm{will}\mathrm{strike}\mathrm{the}\mathrm{ground}. \\ \mathrm{Again}, \\ \mathrm{v}=\mathrm{u}+\mathrm{gt} \\ \mathrm{or}\mathrm{t}=\frac{\mathrm{v}-\mathrm{u}}{\mathrm{g}}=\frac{80-0}{10}=8\sec \\ \mathrm{Thus},\left(\mathrm{i}\right)8\sec \\ \left(\mathrm{ii}\right)80\mathrm{m}/\mathrm{s} \end{gathered}$$