Answer to Question #101039 in Classical Mechanics for archie marney

Question

A christmas present ( modelled as a particle) 0.5 kg is released from rest on the surface of
water in a well. It takes 2 seconds to reach the bottom of the well. Find depth well

Answer 1

Note- Here the question is given incomplete, here the resistive force applied by the water must be given.

Let the resistive force applied by the water is f.

Let the weight of the ball is W

$W-f=ma$

$\Rightarrow 0.5\times9.8 -f= 0.5a$

$\Rightarrow a=\dfrac{4.9-f}{0.5}$

$\Rightarrow a=9.8-2f$

Now,

$h=ut+\dfrac{at^2}{2}$

$h=0+\dfrac{9.8-2f}{2}t^2$

substituting the value of t in the equation

$h=2(9.8-2f)=19.6-4f$ m