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JIPMER2016PhysicsThermal Properties of Matter

A lead bullet penetrates into a solid object and melts. Assuming that 50 % of its kinetic energy was used to heat it, the initial speed of the bullet is (the initial temperature of the bullet is 25^ C and its melting point is 300^ C . Latent heat of fusion of lead =2.5 10^4 ~J / kg and specific heat capacity of lead =125 ~J / kg - K

Options

  1. A100 m/s
  2. B490 m/s
  3. C520 m/s
  4. D360 m/s

Correct answer

B. 490 m/s

Step-by-step solution

Given, S=125 ~J / kg - K =25^ C , =300^ C , m=2.5 10^4 ~J / kg , then 1 2 m v^2 1 2 =m S +mL array rlrl & & v^2 4 & =125(300-25)+2.5 10^4 & & v^2 4 & =59375 & & v^2 & =59375 4 & & v & = 237500 v=487.3 ~m / s & & 490 ~m / s array

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