NEET-XII-Physics
25: Calorimetry
- #13A van of mass 1500 kg travelling at a speed of 54 km h-1 is stopped in 10 s. Assuming that all the mechanical energy lost appears as thermal energy in the brake mechanism, find the average rate of production of thermal energy is cal s-1.Ans : Given:
Mass of van, m = 1500 kg
Speed of van, v = 54 km/h
`` =54\times \left(\frac{5}{18}\right)=15\,\mathrm{\,m\,}/\,\mathrm{\,s\,}``
Total kinetic energy of the van is given by
`` K=\frac{1}{2}m{v}^{2}``
`` K=\frac{1}{2}\times 1500\times {\left(15\right)}^{2}``
`` K=750\times 225``
`` K=168750\,\mathrm{\,J\,}``
`` K=\frac{168750}{4.2}``
`` K=40178.57\,\mathrm{\,cal\,}``
Loss in total energy of the van = 40178 cal
Loss in energy per second `` =\frac{40178}{10}=4017.8``
`` \approx `` 4000 cal./sec
∴ Average rate of production of thermal energy ≈ 4000 cal/sec
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