A 3.0 kg solid disk of radius 0.80 m that is mounted on a horizontal frictionless axis through its center. A light string is wrapped around its rim, and a 1.0 kg box is attached to the other end of the string. The box is released from rest from an unknown height above the floor, and has a speed of 4.2 m/s just as it strikes the floor. Neglect friction and drag. The initial height of the box above the floor is:
A. 0.45 m.
B. 0.90 m.
C. 1.4 m.
D. 2.3 m.
Answer:D
A 3.0 kg solid disk of radius 0.80 m that is mounted on a horizontal frictionless axis through its center. A light string is wrapped around its rim, and a 1.0 kg box is attached to the other end of the string. The box is released from rest from an unknown height above the floor, and has a speed of 4.2 m/s just as it strikes the floor. Neglect friction and drag. The initial height of the box above the floor is:
A. 0.45 m. B. 0.90 m. C. 1.4 m. D. 2.3 m.