# Pressure and mass density

1. Oct 7, 2009

### caitbaby23

1. The problem statement, all variables and given/known data
A spring sticks up from the bottom of the sink, 0.20[m] long ; when a light (ρ=750[kg/m³]) wood block (0.2[m,x]×0.2[m,y]×0.1[m,z]) is attached on top of it, the spring becomes 0.05[m] long.

2. Relevant equations
mass density = mass / volume
Fspring = -ks

3. The attempt at a solution

a) weight of block = 3kg
stiffness of spring???
b & the others.. ??

2. Oct 7, 2009

### gamer_x_

What do you need to determine?

3. Oct 7, 2009

### caitbaby23

a) calculate the weight of the block, and the spring's stiffness.
b) Write the Forces applied to the block if the sink is filled until the block's top is .05[m] below water surface (ρ=1000[kg/m³]).
c) calculate the Pressure Force on block's top and on block's bottom. (Patmosphere=10000[N/m²])
d) What will the spring's length become, when the block is submerged?

4. Oct 7, 2009

### gamer_x_

- for spring stiffness all you need to think about is the formula for the force exerted by a spring. draw your free body diagram. There will only be two forces...

- what do you think adding water does? the question already gives you a great hint in that it gives you the density of water...