# Homework Help: Where is better to put the tube for drinking water better?

1. Dec 19, 2011

### Thoughful

Every one who can answer these 3 questions, help me to understand Physics better.It also help other people who are interested in physics.

1-Imagine you want to drink a glass of water with a straw.Where is better to put the tube for drinking water better?

2-Boats which have engine lurch and the front part of them up when they want to move.It is a logical thing but why are they lurching after some minutes that boat move with permanent speed?

3-If we place a stone on mud, it will sink at certain rate because of its weight. However if we drop the same stone from some unknown height it will sink down twice as fast. What is that height?

I think the second question related to mechanic but my information is so limited, I search in internet and relevant books but i can't solve them. Please help me.

Last edited: Dec 19, 2011
2. Dec 19, 2011

### JHamm

1 - I don't understand, one end in your mouth and the other in the water?
2 - The lurching (bouncing if I understand right) is because of the waves in the water, even boats which are anchored have a gradual rise and fall, now imagine how they would move if they crashed against these gentle waves at 30kms an hour. Once the front end rises it will keep bouncing off the water surface as it lands.
3 - I'm sorry I really don't know what you're asking.

3. Dec 19, 2011

### Nanako

hii ^^ i'm no physicist but i'll try to answer your questions with common knowledge

1. by a tube, i assume you mean something like a drinking straw? to drink the water most efficiently, you would want it todo as little work as possible. this means you want the straw at a slanted angle, as much as possible. If modifying the glass is allowed, i'd suggest making a hole in the bottom and holding it above your head as you drink straight downwards. but failing that, just tilt the straw. it also needs to be tilted so that there's space at the end for water to get in.

2. I would guess the force of hitting waves in the water pushes it upwards. i'm not sure what you mean by permanant speed.

3. i can't make any sense of this question. i guess english is not your first language :(

4. Dec 19, 2011

### Thoughful

I don't know how should I say for the third question but your guess is correct.English is my second language.

5. Dec 19, 2011

### Staff: Mentor

Why not draw a diagram to describe the problem and post it?

6. Dec 19, 2011

### Staff: Mentor

3-If we have a global thing like a stone and put it in some mud, the thing drown in mud. Now if we like that the drowning of the thing redoubled, From how far should we fall the thing?

With respect to your #3 question, are you saying:

If we place a stone on mud, it will sink at certain rate because of its weight. However if we drop the same stone from some unknown height it will sink down twice as fast. What is that height?

Does that sound right?

If so then you're treating the mud as a form of resistance similar to air resistance and as such you would be interested in the stone's terminal velocity as it traversed the mud on its way to the bottom.

7. Dec 19, 2011

### Thoughful

8. Dec 20, 2011

### PeterO

Lets invent some figures here:

Suppose a stone sinks into mud at the rate of 1 cm per second.

If the stone was dropped from a height, it may arrive at 5 m/s.

On contact with the mud, it will slow rapidly - until, eventually, it is also descending at 1 cm per second.

So the question is: did you want it to be traveling at 2 cm per second when it hit the mud [don't drop it from very high!] or are you trying to work out how long before it slows to terminal velocity of 1 cm per second, would it be still traveling at 2 cm per second.

I use those assumed values just to make communication easier.