# Homework Help: Mechanic fluid

1. Nov 25, 2007

### logglypop

1)A cup contain 15cm lvl water. A 29cm straw is place into the cup, at the end of the straw is 1cm from the bottom. If a person sucks on the straw, what gauge pressure is needed at the top of the straw to allow the water to run out of the top and into his mouth.

P=pgh
1000(9.8) .29 = 2842 Pa

2) Approximately how deep below the surface of the ocean must a diver go before the absolute pressure on him 2atm.

P=P0 + pgh
2atm= 1atm + 1000(9.8)h 1atm=100000 Pa
100000 Pa= 1000(9.8)h
h=10m

3) A body having a density of 300kg/m^3 is floating in a container of liquid. If 1/3 of the volume of the body remains above the surface of the liquid, what is the density of the liquid?
1/2*300=100kg/m^3
100+300= 400 Kg/m^3

2. Nov 25, 2007

### logglypop

3. Nov 26, 2007

### logglypop

anyone?

4. Nov 26, 2007

### spirit89

1. P0 = P+ pgh
P = P0 - 1000(9.8) .29

5. Nov 26, 2007

### spirit89

P=pgh
2atm=1000(9.8)h shud nt take atmosph press. because inside water it acts in all dir. hence cancels

6. Nov 26, 2007

### spirit89

3. P*2/3=300
3/2*300=450

7. Nov 26, 2007

### logglypop

ty
I got the last 1 still trying to figure out and may be u can help
10kg raft made of driftwood w/ specific gravity .60 floats on the surface of a calm pond. Density of water = 1000 kg/m^3
Calculate the volume of the raft

Im not sure if the problem missing some unit
I need Density of the raft to calculate the Volume
I dont know how to get there. Any idea?