Question

The instantaneous velocity of a point on the outer edge of a disk with a diameter of 4 m that is rotating at 120 revolutions per minute is most nearly:

• A. 4 m/s
• B. 6 m/s
• C. 12 m/s
• D. 25 m/s
• E. 50 m/s

Answer 1

The correct option is D 25 m/s

Radius of the disk $r=\frac{d}{2}=\frac{4}{2}=2$ m

Frequency of rotation $f=120$ rpm $=\frac{120}{60}=2$ rps

Thus instantaneous linear velocity $v=rw=r\left(2\pi f\right)=2\times (2\pi \times 2)\approx 25$ m/s