Plotting Y as a Function of Time: MATLAB Homework Help

[bcjochim07]

Homework Statement

A 75.0 g ball with radius 10cm is dropped. I am supposed to write a program that plots y as a function of time, including acceleration due to gravity and drag force of D=0.25*area*velocity.

Homework Equations

The Attempt at a Solution

Here's what I tried:

>> n=21;
>> t=zeros(1,n);
>> v=zeros(1,n);
>> y=zeros(1,n);
>> h=0.5;
>> g=-9.80;
>> m=0.075;
>> A=pi*0.10*0.10;
>> for i = 2:n
t(i)=(i-1)*h;
fdrag=0.25*A*v*v;
adrag=fdrag/mass;
a=adrag+g;
v(i)=v(i-1)+a*h;
y(i)=y(i-1)+v(i-1)*h+0.5*a*h*h;
end;
? Error using ==> mtimes
Inner matrix dimensions must agree.
>>

t is time, h is time increment, m is mass, a is total acceleration, A is area

I don't understand the error that I am making. Could someone please help me?

 

[cjl]

Well, the cause for that error is that the default multiplication operation in Matlab is the matrix multiply. For something like this, you do not want the matrix multiplication - you want to extract just the item you are currently working on and use that value. There are some other problems too, but we can start by fixing that.

Also, it is always best to have a thorough understanding of exactly what you are trying to get the code to do in each section before coding - do you have all of that worked out?

 

[CEL]

Complementing what cjl said, you should make:
fdrag=0.25*A*v(i-1)*v(i-1);