Question

A submersible is lowered into the sea at a speed of $4m/s$ and comes to rest with uniform retardation at a distance of $10m$ below the surface, calculate (a) Its retardation and (b) the time it takes to come to rest.

Answer 1

R.E.F image

(I) using $v^2-u^2=2as$

$0^2-4^2=2\times a\times 10$

$-16=20\times a$

$a=-0.8m/s^2$

retardation $0.8m/s^2$

(II) using $v=u+at$

$0=4+0.8\times t$

$t=\frac{40}{8}=5$

time taken $=5sec$