# Distance and speed in spud gun

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1. Nov 28, 2015

### Mirzet99

1. The problem statement, all variables and given/known data
I have to calculate the speed with which a spud gun fires a bullet. The lenght of barrel is 1 meter.

2. Relevant equations
v=s/t , where v=velocity; s=distance; t=time

3. The attempt at a solution

NOTE: I will easily calculate distance. I have spud gun but I don't know the way how to calculate that speed which is not average speed of bullet.

2. Nov 28, 2015

### haruspex

You cannot calculate anything without some data. The length of the barrel is clearly not enough. What else do you know or can know?

3. Dec 2, 2015

### Mirzet99

I don't know anything else. My profesore wants me to do that but he doesn't want to tell me how. I think he doesn't know also..

4. Dec 2, 2015

### Staff: Mentor

Please describe how a spud gun works. (I know how a spud gun works. I'm just asking you to describe it in words). I'm sure that will give you some ideas on what you need to do to answer this question.

Chet

5. Dec 4, 2015

### Mirzet99

In barrel, I put potato. In this lower,biggest part,I put gasoline and with igniter, I burn it. Explosion happens and that gas wants to spread. But it is closed from all sides,expect this one where is potato. That's the way how it works.

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6. Dec 4, 2015

### Staff: Mentor

If I remember correctly, the spud is situated near the forward end of the barrel, correct? How far back is typical?

You need to know the volume of the chamber behind the spud. Approximately what volume is that (of air to start with). You also need to know approximately how much gasoline is injected into the chamber. So, how much??

What is the balanced equation for the reaction of air and gasoline? What is the heat of reaction of gasoline and oxygen? Based on the stoichiometry of the reaction, how many moles of gas will be in the chamber after all the gasoline has burned?

This should get you started.

Chet

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