Hi there!
Recall the equation for centripetal force:

We can rearrange the equation to solve for 'r'.
Multiply both sides by r:

Divide both sides by Fc:

Answer:


Explanation:
1 full revolution is
let \theta be the angle of Ron's position.
At t = 0. 
one full revolution occurs in 12 sec, so his angle at t time is

r is radius of circle and it is given as


for r = 30 sec


however, that is centered at (0,0) and the positioned at time t = 0 is (30,0). it is need to shift so that the start position is (30,45). it can be done by adding to y


Answer:
C
Explanation:
velocity = displacement (m) / change of time (s)
velocity = (400 + 300) / (100 + 400)
velocity = 1.4 m/s