Jagged Sine Wave Results

For my Vibrations class, I was asked to plot a simple system responce seen in the image below, but the plot seems rather jagged. Is there something I am not inputting correctly?

Answer 1

[David Hill]

t=0:.001:1;%need smaller increment
theta=.1*sin(20*t+pi/2);
plot(t,theta);

Answer 2

[VBBV]

%if true
  % code
% end
t = 0:0.005:1;
theta = 0.1*sin((20*t)+(pi/2));
plot(t,theta);