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The speed of bicycle decreases from …

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The speed of bicycle decreases from 18 to 9 km/h. If the total mass of the cyclist including the bicycle is 70 kg. Calculate the work done in overcoming the friction offered by the brake and the road. Does the K.E. of the system also reduce to half its initial velocity?
  • 1 answers

Sia ? 2 years, 10 months ago

m = 70 kg
v = 9 kmph = 9 * 5/18 = 2.5 m/s
u = 18 kmph = 18 * 5/18 = 5 m/s
Work done  = change in kinetic energy
= initial KE - final KE
= 1/2 m u² - 1/2 m v²
= 1/2 * 70 * 5² - 1/2 * 70 * 2.5²
= 875 J - 218.75 J  = 656.25  J
The speed has come down to half its value.  But the Kinetic energy becomes 218.75/875 = 1/4 th of inital KE.

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