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Question
A 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.
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Solution
Given:-
Mass of van, m = 1500 kg
Speed of van, v = 54 km/h
`=54xx(5/18)=15"m/s"`
Total kinetic energy of the van is given by
`K=1/2"mv"^2`
`K=1/2xx1500xx(15)^2`
K = 750 x 225
K = 168750 J
`K=168750/4.2`
K = 40178.57 cal
Loss in total energy of the van = 40178 cal
`"Loss in energy per second" =40178/10=4017.8approx4000"cal./sec"`
∴ Average rate of production of thermal energy ≈ 4000 cal/sec
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