The kinetic energy of an object of mass, m moving with a velocity of 5 m s–1 is 25 J. What will be its kinetic energy when its velocity is doubled? What will be its kinetic energy when its velocity is increased three times?

NCERT Class IX
Sciences - Main Course Book

Chapter 11. Work and Energy

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2015-05-22T13:35:11+05:30

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K. E.  =  1/2 m v^2  =  1/2 * m 5^2  = 25 Joules
         =>  m = 2 kg

When the velocity becomes double:  ie.,  10 m/s

K. E.   =   4 times previous value = 4 * 25 J = 100 J
                 or, 1/2 m v^2= 1/2 * 2 kg * 10^2  Joules      =  100 Joules

  v  =  3 times = 15 m/s
KE will become  9 times original value ,as  KE is proportional to the square of the velocity
 
   K. E. =  1/2 m v^2 = 1/2 * 2 kg * 15^2  =  225 Joules

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