- #1

- 50

- 0

## Homework Statement

a body of mass 6.0kg and density 450kg/m^3 is dropped from rest at a height of 7.5m into a lake. Calculate

1. the speed of the body just before entering the lake

2. the acceleration of body while its in the lake

3. the maximum depth to which the body sinks before returning to surface.

Neglect any surface tension or air resistance.

## The Attempt at a Solution

s=0.5gt

^{2}

sub s=7.5m, g=9.81, t=1.2365s

then v=gt, v=12.131m/s

2. F

_{float}= ρgV, net force= F

_{float}-mg

V=6.0/450=1/75, net force=-(1000 x 9.81 x 1/75 -6.0 x 9.81)=-71.94

then F=ma, a=-71.94/9.81=-7.3333m/s

^{2}

for me, down is positive, up is negative

3. using v

^{2}=v

_{0}

^{2}+2as, v=0 when the body stops sinking.

s=10.034m, which is the distance sank.

Gahh I really think this question is rather easy, have not done dynamics for sometime, have given everything back to the teacher, sadly:(