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Kinetic Theory — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysicsKinetic Theory1 Mark
Question
A brick weighing 4.0kg is dropped into a 1.0m deep river from a height of 2.0m. Assuming that 80% of the gravitational potential energy is finally converted into thermal energy, find this thermal energy is calorie.
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Answer

Given, Mass of the brick, m = 4kg Total vertical distance travelled by the brick, h = 3m Percentage of gravitational potential energy converted to thermal energy = 80 Total change in potential energy of the brick = mgh = 4 × 10 × 3 = 120J Thermal Energy $=120\times\frac{80}{100}=96\text{J}$ Thermal energy in calories is given by,$\text{U}=\frac{96}{4.2}=22.857\text{cal}\approx23\text{cal}$

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