A stone is dropped into a lake creating a circular ripple that travels outward at a speed of 40 cm s a Express the radius r of this circle as a function of the time t in seconds r t b If A is the area of this circle as a function of the radius find A o r Aor t Interpret the answer found in part b O This formula gives the radius of the rippled area in cm at any time t This formula gives the circumference of the rippled area in cm at any time t O This formula gives the extent of the rippled area in cm at any time t