Cuesta College, San Luis Obispo, CA
The "hammer" used in a hammer throw competition can be approximated[*] as a ball spun in a circle at the end of a chain of negligible mass, with a rotational speed of 24 rad/s. The rotational inertia of the ball and chain system is 11 kg·m2. (Ipoint mass = m·r2.) If the mass of the ball is 7.3 kg, the length of the chain is:
(A) 0.66 m.
(B) 1.2 m.
(C) 1.5 m.
(D) 2.2 m.
Correct answer (highlight to unhide): (B)
The rotational inertia of a point mass m and moving in a circle of radius r is:
Ipoint mass = m·r2,
such that solving for the radius (which would be the length of the chain):
r2 = Ipoint mass/m,
r = √(Ipoint mass/m),
r = √((11 kg·m2)/(7.3 kg)) = 1.227537907792867 m,
or to two significant figures, the chain length is 1.2 m.
(Response (A) is m/Ipoint mass; response (C) is √(m·g/Ipoint mass); response (D) is m·g/Ipoint mass.)
Sections 70854, 70855, 73320
Exam code: quiz05b0oM
(A) : 4 students
(B) : 32 students
(C) : 14 students
(D) : 5 students
Success level: 58%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.38