question_answer

A stone is thrown vertically upwards with a velocity of 34.3 m/s from the top of a cliff 147 m high. In what time does it reach the foot of the cliff?

Answer:

\[u=34.3\,m/s\] \[h=147\,\,m\] \[g=9.8m/{{s}^{2}}\] \[t=?\] For a body projected up from the top of the tower, \[h=-ut+\frac{1}{2}a{{t}^{2}}\] \[\Rightarrow 147=-34.t+4.9\,\,{{t}^{2}}\] \[(or)\,\,4.9\,{{t}^{2}}-34.3t\,-147=0\] \[i.e.\,\,{{t}^{2}}-7t-30=0\] \[i.e.\,\,(t-10)(t+3)=0\] \[i.e.\,\,t=10s\]