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NEET2015PhysicsThermal Properties of MatterActual

A lead ball at 30^ C is dropped from a height of 6.2 km . The ball is heated due to the air resistance and it completely melts just before reaching the ground. The molten substance falls slowly on the ground. If the specific heat of lead =126 Jkg ⁻¹⁰ C ⁻¹ and melting point of lead =130 ^ C and suppose that any mechanical energy lost is used to heat the ball, then the latent heat of fusion of lead is

Options

  1. A2.4 10^4 Jkg ⁻¹
  2. B3.6 10^4 Jkg ⁻¹
  3. C7.6 10^2 Jkg ⁻¹
  4. D4.2 10^3 Jkg ⁻¹

Correct answer

A. 2.4 10^4 Jkg ⁻¹

Step-by-step solution

The gravitational potential energy of the ball =m g h aligned & =m 10 6.2 10^3 & =m 62 10^4 ~J aligned Now energy required to take ball from 30^ C to 330^ C is m 126 300=m 37800 Energy required to melt the ball =mL where, L= latent heat aligned m 6.2 10^4 L & =m 37800+mL L & =2.4 10^4 Jkg ⁻¹ aligned

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