Question

A stone is dropped from a certain height which can reach the ground in $5\,s$. If the stone is stopped after $3\, s$ of its fall and then allowed to fall again, then the time taken by the stone to reach the ground for die remaining distance is

• A. 2 s
• B. 3 s
• C. 4 s
• D. None of these

Answer 1

Answer: (C)

4 s

Answer 2

From, $s=ut+\frac{1}{2}at^{2}$ Distance covered in $5s$ $s=0+\frac{1}{2}\times 10\times 5^{2}=125\,m$ Distance covered in $3\,s$ $s=0+\frac{1}{2}\times 10\times 3^{2}=45\,m$ Distance

to be covered $125-45=80\,m$ From, $s=ut+\frac{1}{2}at^{2}$ $80=0+\frac{1}{2}\times 10\,t^{2}$ $t^{2}=\frac{80}{5}=16$ $t=4\,s$