# Homework Help: Guass's law & protons

1. Oct 22, 2008

### Gaara09

1. The problem statement, all variables and given/known data
Hey , I am a new member Here . I am having some diffuculties , i did one problem and still 1 problem i can't do it coz it seems very hard as i am new to gauss's Law

I am doing college physics II , protons are projected with initial speed of v0 = 9550m/s into a region in which a uniform electric field , E= 720N/C is present . the protons are to hit a target that lies a horizental distance of 1.27mm from the point at which the protons are lauched.
Find the two projections angles that will result in the hit .

b- the total duration of flight for each of thse two trajectoires.

3. The attempt at a solution
I tried to do these E= K.(q)/r^2 , E.A.cos (x). well i don't have any clue....

I hope you can help me

Thanks

2. Oct 22, 2008

### LowlyPion

Welcome to PF.

You can treat it like a traditional projectile range problem.
http://www.physics.ubc.ca/~outreach/phys420/p420_00/darren/web/range/range.html

To figure your acceleration you can use:

$$\vec{F} = q * \vec{E} = m * a$$

3. Oct 22, 2008

### Gaara09

Thank you so Much .

http://www.physics.ubc.ca/~outreach/phys420/p420_00/darren/web/range/range.gif

sorry i am not very good in physics , do i need to use this ?
we have x= 1.27mm / so i can get the sin ?

4. Oct 22, 2008

### LowlyPion

Once you figure g you can solve for θ.

5. Oct 22, 2008

### Gaara09

g is 10 right ?

6. Oct 22, 2008

### LowlyPion

No. g = a. That is the acceleration from your E-field. It is a function of the charge of the proton and its mass. You have to figure that out.

I said you could treat it LIKE a projectile range equation. Only you aren't concerned with gravity. You are concerned with the constant acceleration due to the E-field.

7. Oct 22, 2008

### Gaara09

aha ok Thanks , got it Now .

Gonna solve it now , Thanks again !!