A disc of radius 2 m and mass of 100 kg roll on a horizontal surface, its center of mass has speed of 2 cm/s, how much work is needed to stop it?
Correct answer: B. 3 J
- A. 1 J
- B. 3 J
- C. 30 J
- D. 2 J
Explanation
Work done to stop the disc = change in total kinetic energy of disc Final KE = 0 Initial KE = Translational K.E + Rotational K.EInitial KE= ½mv2 + ½ Iω2 Initial KE= ½mv2 + ½ x mR2 / 2 x (v/R)2Initial KE=½mv2 + ¼ mv2 = ¾ mv2Initial KE= =¾ ×100× (20×10-2)2 ΔKE ="3J"
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About Kinetic Energy
Kinetic energy is the energy of motion, given for a nonrelativistic object by K = ½mv², so it depends on mass and the square of speed. Questions connect kinetic energy with work through the work energy theorem, calculate changes in kinetic energy, and distinguish it from momentum and potential energy.
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