A stone weighing 2 kg falls from the top of a tower 40 metre heigh and burries itself 1m deep in sand. The time of penetration is :

Options

A. `1/(15)s`
B. `1/(13)s`
C. `1/(14)s`
D. None of these

Answer

c

Explanation

Here let v be the velocity of strike , then
`v^2=2xx9.8xx40`
or v=28 ms
Now for the sand we have
`v^2 -u^2 =2 as`
`0-(28)^(2)=2axx1`
`a=-((28)^2)/(2)`
`:. T=(2xx28)/((28)^(2))=1/14 s`