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NCERT/CBSE PHYSICS CLASS 11 textbook
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Answers to NCERT/CBSE PHYSICS Class 11(Class XI)textbook Exercise and
Additional exercise
CHAPTER SEVEN
SYSTEM OF PARTICLES AND ROTATIONAL MOTION
EXERCISES
(For simplicity in numerical calculations, take g = 10 m s-2)
7.32 Read each statement below carefully, and state, with reasons, if it
is true or false;
(a) During rolling, the force of friction acts in the same direction as
the direction of motion of the CM of the body.
(b) The instantaneous speed of the point of contact during rolling is
zero.
(c) The instantaneous acceleration of the point of contact during rolling
is zero.
(d) For perfect rolling motion, work done against friction is zero.
(e) A wheel moving down a perfectly frictionless inclined plane will
undergo slipping (not rolling)
motion.
7.32
Solution:
(a)During rolling the direction of friction is against the direction of relative slipping
of point in contact with the ground. As the direction of point of contact is opposite to
direction of motion of CM it can be concluded that given statement is true.
(b)As the point of contact does not slip with respect to ground,the instantaneous
velocity of the point of contact during rolling is zero.
(c)As the motion continues to be rotational hence acceleration of point
is not zero.So the statement is false.
(d )The statement is true.As the point of contact stays at rest with respect to the surface,no
work is done by the friction.
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