Q13 of 28 Page 52

With reference to Fig. 7.6 of a cube of edge an and mass m, state whether the following are true or false. (O is the centre of the cube.)


Option a is false since perpendicular axes theorem is applicable only for laminar/planar objects.

Distance between z and z’


Applying parallel axis theorem



So option b is correct.


Z’’ and z are skew lines. That is, they are neither parallel nor perpendicular. So option c is incorrect as it is using parallel axis theorem.


Since the cube is symmetric, moment of inertia about x and y axis are equal. So, correct options are b and d.

More from this chapter

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11

The net external torque on a system of particles about an axis is zero. Which of the following are compatible with it?

 12

Figure 7.5 shows a lamina in x-y plane. Two axes z and z′ pass perpendicular to its plane. A force F acts in the plane of lamina at point P as shown. Which of the following are true? (The point P is closer to z′-axis than the z-axis.)


 14

The centre of gravity of a body on the earth coincides with its centre of mass for a ‘small’ object whereas for an ‘extended’ object it may not. What is the qualitative meaning of ‘small’ and ‘extended’ in this regard? For which of the following the two coincides? A building, a pond, a lake, a mountain?

 15

Why does a solid sphere have smaller moment of inertia than a hollow cylinder of same mass and radius, about an axis passing through their axes of symmetry?