Question

A thread is being pulled off a spool at the rate of 40 cm per second. Find the radius of the spool

if it makes 150 revolutions per second for 10 seconds.
How can I find this answer and what is the answer

Answer 1

r = 0.0424 cm (3sf)

Explanation:

it makes 150 rev/sec

1 revolution = 1 circumference = 2pi*r

so every second the spool goes through 2*pi*r*150 of distance

we know that the rate of pulling is 40cm/sec

so 2pi*r*150 = 40

r = 40/(2pi*150), which is 0.04244131816 cm.

check: Circumference is 2pi*r = 0.2666

now multiply by 150rev/sec = 40 cm/sec