NCERT CLASS IX - Science Textbook
Chapter 11 - Work and Energy

The kinetic energy of an object of mass, mmoving with a velocity of 5 m s - '1is 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?

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2015-05-16T17:44:04+05:30

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Velocity = v = 5 m/s
mass = m

Kinetic energy = 1/2 m v² 
  1/2 m * 5² = 25 Joules
  =>   m = 2 kg

When the velocity v is doubled,  since there is  v²  in the expression for KE.,  KE becomes 2² = 4 times.
   So  the KE will be 25 J * 4 = 100 Joules.

when the velocity is increased to 3 times its original value:  ie., 15 m/sec,  its KE is 3² = 9 times ,  hence,  9 * 25 J = 225 Joules.

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