User input changes circle radius and velocity

I want to make this so that when a user inputs a new radius, the circle changes accordingly, but I'm not sure how to go about it.

v=input('Please provide a particle velocity: \n');
r=input('Please provide a radius: \n');

 x0 = 0;
 y = 3;
                   
 for time=-7:0
 x = x0(1,:) + v*time; 
 plot(x, y,'ro');         % particle moving along the x axis
 axis([-3 3 -7 3])
 drawnow();
 pause(.5)
 end
t = linspace(0,2*pi);
x = cos(t);
y = sin(t);
plot(3*x,3*y)       % current plot circle - radius 10
axis equal
hold on
for t0 = t
    h = plot(3*sin(t0),3*cos(t0),'or');         % particle moving around the circle
    pause(0.3)
    delete(h)

end
hold off

Answer 1

[KSSV]

You are using the radius while calculating the coordinates of circle.

v=input('Please provide a particle velocity: \n');
r=input('Please provide a radius: \n');

 x0 = 0;
 y = 3;
                   
 for time=-7:0
 x = x0(1,:) + v*time; 
 plot(x, y,'ro');         % particle moving along the x axis
 axis([-3 3 -7 3])
 drawnow();
 pause(.5)
 end
t = linspace(0,2*pi);
x = r*cos(t);  % use the radius here 
y = r*sin(t);  % use the radius here 
plot(x,y)       % current plot circle - radius 10
axis equal
hold on
for t0 = t
    h = plot(3*sin(t0),3*cos(t0),'or');         % particle moving around the circle
    pause(0.3)
    delete(h)

end
hold off

Answer 2

[VBBV]

v=10;%input('Please provide a particle velocity: \n');
r=5; %input('Please provide a radius: \n'); e.g. radius here 

 x0 = -2; % offset 
 y0 = 3;  % offset 

t = linspace(0,2*pi);
x = x0 + r*cos(t);  % use the radius here with an offset 
y = y0 + r*sin(t);  % use the radius here with an offset 
plot(x,y)       % current plot circle 

x = r*cos(t);  % use the radius here without an offset 
y = r*sin(t);  % use the radius here without an offset 
hold on
plot(x,y,'r')

you can also try using an offset distance for centre to plot