System of Particles and Rotational Motion - Result Question 71

78. A disc of radius 2m and mass 100kg rolls on a horizontal floor. Its centre of mass has speed of 20cm/s. How much work is needed to stop it ?

[2019]

(a) 3J

(b) 30kJ

(c) 2J

(d) 1J

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Answer:

Correct Answer: 78. (a)

Solution:

  1. (a) Work done to stop the disc = change in total kinetic energy of disc

Final KE=0

Initial KE= Translational K.E. + Rotational K.E.

=12mv2+121ω2

=12mv2+12×mR22×(vR)2

=12mv2+14mv2=34mv2

=34×100×(20×102)2=3J

|ΔKE|=3J



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