JEE Main 2022 · 27 Jun · Shift 2 · Physics Q39

← JEE Main 2022 · 27 Jun · Shift 2

PhysicsSingle correct+4 / -1Question 39 of 90

A lead bullet penetrates into a solid object and melts. Assuming that 40% of its kinetic energy is used to heat it, the initial speed of bullet is :

(Given, initial temperature of the bullet = 127°C, Melting point of the bullet = 327°C, Latent heat of fusion of lead $=2.5\times10^4$ J kg $^{-1}$ , Specific heat capacity of lead = 125 J/kg K)

125 ms

^{-1}

500 ms

^{-1}

250 ms

^{-1}

600 ms

^{-1}

Answer and worked solution

Official answer: B

Heat needed per kg: $125\times200+2.5\times10^4=5\times10^4$ J.

Speed. $0.4\cdot\frac12v^2=5\times10^4$ , so $v^2=2.5\times10^5$ , $v=500$ m s $^{-1}$ .

(B)

Topics:Latent heat and phase change Calorimetry and specific heat

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JEE Main 2022 · 27 Jun · Shift 2, Physics question 39