Page 22 - SP015 Past Years PSPM Chapter 6 -14 Ver 2020

PHYSICS PSPM SEM 1 1999 - 2017

PSPM JUN 2000/2002 SF025/2 No. 9(c)

32. Two identical balls 0.5 kg each is tied to both ends of a light rod of 1.0 m long. A
member of a circus held the rod at the centre and rotates it.

(a) What is the moment of inertia of the ball system about its axis of rotation? [3 m]
(b) If the rod is rotated 30 rotations per minute, what is the angular momentum?
[2 m]
(c) Determine the kinetic energy of the system. [2 m]

PSPM 2001/2002 SF015/2 No. 11(b)(i), (iii)

33.
rotation axis

marble R track of cone

60

FIGURE 8.13

A small track of conical shape can rotate about its axis has angle of 60 as shown in
FIGURE 8.13. A marble of mass m is placed on the track. When the track rotates with
an angular velocity of , the marble does not move at a distance R.

(a) Draw all the forces that act on the marble. [3 m]

(b) If the cone stops rotating, the marble will roll down. Calculate the acceleration of
the marble while going down the track of the cone. Given moment of inertia of the
2
2
marble is mr where r is the radius of the marble. [5 m]
5

PSPM 2002/2003 SF017/2 No. 12(c)

2
34. A disc of moment inertia 0.05 kg m is fixed on an axis of rotation that rotates at a rate
of 30 rotations per second. Then its motion is slowed down uniformly until it stops. If
the disc rotates 60 rotations before it stops, calculate
(a) the angular acceleration of the disc. [3 m]

(b) the time taken for the disc to stop. [3 m]
(c) the change of kinetic energy of the disc rotation. [3 m]

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