A stone of mass 100g is whirled in a horizontal circle of diameter 80.0cm at 150 revolutions per 5 minutes. Calculate the frequency and centripetal force.

The shadow of the stone moving in a horizontal circle undergoes Simple Harmonic Motion (SHM) on the wall.

• The amplitude of this motion is the radius of the circle, $A = r = 0.40 \text{ m}$.
• The period of the motion is $T = \frac{1}{f} = \frac{1}{0.5 \text{ Hz}} = 2 \text{ s}$.
• The graph will be sinusoidal, showing the shadow's distance from the center of its oscillation over time. For two cycles, the graph will span $2T = 4 \text{ s}$.

Here is a description of the sketch:
The graph will have "Time (s)" on the x-axis and "Distance from center (m)" on the y-axis.
The y-axis will range from $-0.40 \text{ m}$ to $+0.40 \text{ m}$.
The x-axis will range from $0 \text{ s}$ to $4 \text{ s}$.
The curve will be a sine wave (assuming the shadow starts at the center of its oscillation at $t=0$) or a cosine wave (if it starts at maximum displacement).
It will complete one full oscillation (return to its starting position and direction) every $2 \text{ s}$. So, at $t=0, 2, 4 \text{ s}$, the distance will be $0 \text{ m}$ (if starting from center). At $t=0.5, 2.5 \text{ s}$, the distance will be $+0.40 \text{ m}$. At $t=1.5, 3.5 \text{ s}$, the distance will be $-0.40 \text{ m}$.