Question

Please help with question 4A,B please Thank you

Answer 1

Given

• C(t) = 40 cm + t·(2/5 cm/s) . . . circumference of a circle vs time

Find

• dr/dt for radius r
• r at t=4 seconds

Solution

The circumference and radius of a circle are related by

... C = 2πr

so the radius in terms of circumference is

... r = C/(2π)

... r(t) = (40 +0.4t)/(2π) = (1/π)(20 cm + 0.2t cm/s)

Then dr/dt is

... dr/dt = 0.2/π cm/s

And the radius at t=4 s is

... r(4) = (1/π)(20 + 0.2·4) cm

... r(4) = 20.8/π cm