Question

Can you please help me solve (d) ?
https://www.dropbox.com/s/kj9q32u5cwh0jir/Screenshot%202013-11-05%2009.06.07.jpg

Answer 1

@dumbcow do you know this by any chance ?

Answer 2

how fast is stone moving? or how big is the stone?

Answer 3

20m/s

Answer 4

hmm but that is same as cyclist? im not getting how to come up with unit vector at each point A,B,
maybe someone else should help you on this one

Answer 5

ok man np

Answer 6

I'm going to assume the radius of the circle is the rope itself and the circle is it's path. Am I right?

Answer 7

If so:
A) The velocity is always tangential to the circle. The acceleration is always centripetal. Think of it as if the stone is with a circular orbit around the center of the rope.

B) 60 cycles in one minute, means it takes one second per rotation. So It's period of motion is T=1 s.

C) \[\omega = \frac{ 2 \pi }{ t }= 2 \pi \]
\[a = \omega ^{2} r\]

D) \[v = \omega r\]
If it's in B, the vector is perpendicular to the vector of the cyclist, so it doesn't change.
If it's in A, the vector is shifted due to how the cyclist views it's motion, and it's relative velocity is the difference between their velocities.

Funfact: In the cyclists mark of reference, the motion of the stone isn't a circle, it's an ellipse that you can get by squishing the circle by the sides!
It's like if the circle was scaled in one direction. (If the cyclist was moving at 45 degrees from teh horizong, practically flying, the scaling would be in both directions and you'd just get a smaller circle!)