Question

Meghan sets up her model train on a circular track that is 1 metre wide and that sits in her bedroom doorway, half in her bedroom and half in the hallway. Each round trip takes 2 seconds, and the train starts as far into the bedroom as possible. How deep into her bedroom the train engine is in terms of time is modelled by which equation?

Answer 1

Answer:

We have a circular track that is 1 meter wide, which would mean that the diameter is equal to 1 meter.

First, we want to define this problem as a one dimensional problem. The position 0 is in the doorway, the bedroom is the positive axis, and the hallway is the negative side.

P(t) = R*cos(c*t) + R*sin(c*t).

Where R is the amplitude, in the case of the circular motion, R is equal to the radius.

If the diameter is 1m, the radius is 1m/2 = 0.5m

The equation now is:

P(t) = 0.5m*cos(c*t) + 0.5m*sin(c*t).

We also know that for t = 0s, the train is as far into the bedroom as it can, the maximum position is P = 0.5m

Then  we have:

P(0s) = 0.5m*1 + 0.5*0 = 0.5m

And we also know that the period is t = 2seconds.

The period for the sine and cosine functions is 2*pi, then:

c*2s = 2*pi

c =pi/s

The function now is:

P(t) = 0.5m*cos(t*pi/s) + 0.5m*sin(t*pi/s)

When this function is positive, this means that the train is inside her bedroom, when the function is negative, the train is outside the bedroom, when P(t) = 0, the train is in the doorway.