Question

Problem 2. (based on Young & Freedman 9.47) A frictionless pulley has the shape of a uniform solid disk of mass 2.50 kg and radius .0200 m. A stone of unknown mass is attached to a very light wire that is wrapped around the rim of the pulley. When the system is released from rest, the stone accelerates downward at 5.9 m/s 2 (a) What is the angular acceleration of the pulley? Answer: 295 rad/s 2 (b) Find the torque on the pulley from the wire. Answer: .148 Nm (c) What is the tension in the wire? Answer: 7.38 N (d) Find the mass of the stone. Answer: 1.89 kg I can't find the right answer for (d)

Answer #1

**Given**

** mass of solid disc m = 2.5 kg, radius r =
0.02 m
mass of stone M= ?**

** when stone released from rest ,
accelerating 5.9 m/s2so the angular acceleration is a = r*alpha
==> alpha = a/r = 5.9/0.02 = 295 rad/s**

**b)
Torque T = I*alpha
= 0.5*mR^2*alpha
= 0.5*2.5*0.02^2*295 N
= 0.1475 Nm
c)tension in the wire = 7.38 N**

**d)mass of stone M =?**

** tension T = Mg ==> M = T/g = 7.38/9.8 kg
= 0.753 kg**

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