A physics student is standing on an initially motionless, frictionless turntable

Question

A physics student is standing on an initially motionless, frictionless turntable with rotational inertia 0.31 kg m2. He's holding a wheel of rotational inertia 0.22 kg-m2 spining at 129 rpm about a vertical axis, as we showed in Fig. 11.8. When he turns the wheel upside down, student and turntable begin rotating at 75 rpm The student flips over the moving wheel, and thereby reverses its angular momencum. The angular momencum of the system however, is conserved, so what happens to the studem The student stands on a stationary turntable holding a horizontal bicycle wheel that rotates counterctockwise. and the turntable? Figure 11.8 (a) What is the student's mass, considering him to be a cylinder 30 cm in diameter? kg (b) How much work did he do in turning the wheel upside down? Neglect the distance between the axes of the turntable and wheel.

Explanation / Answer

L0 = 0.22 * 129 rpm

If Itot is the total moment of inertia about the z-axis,

LZ = 2 * L0

LZ = Itot (75 rpm) =  2 * 0.22 * 129 rpm

Itot = 0.7568 kg.m2

(1/2) M (0.15 m)2 = (0.7568 - 0.31)

M = 39.71 kg

----------------------------------------------

W = delta K = 1/2 * Itot * w2

= 1/2 * 0.7568 * (75 pi / 30 s)2

= 23.34 J

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.