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NEET 2009
Exam
NEET
Year
2009
Subject
Physics
Chapter
Work, Power and Energy

NEET 2009 · Physics · Work, Power and Energy

A body of mass 1 ~kg is thrown upwards with a velocity 20 ~ms^ -1 ....

A body of mass 1 kg1 \mathrm{~kg} is thrown upwards with a velocity 20 ms−120 \mathrm{~ms}^{-1}. It momentarily comes to rest after attaining a height of 18 m18 \mathrm{~m}. How much energy is lost due to air friction ? (g=10 ms−2)\left(\mathrm{g}=10 \mathrm{~ms}^{-2}\right)

Options

  1. A20 J20 \mathrm{~J}
  2. B30 J30 \mathrm{~J}
  3. C40 J40 \mathrm{~J}
  4. D10 J10 \mathrm{~J}

Correct answer

A. 20 J20 \mathrm{~J}

Step-by-step solution

Key Idea The energy lost due to air friction is equal to difference of initial kinetic energy and final potential energy. Initially body posses only kinetic energy and after attaining a height the kinetic energy is zero. Therefore, loss of energy =KE−PE=\mathrm{KE}-\mathrm{PE}=12mv2−mgh=12×1×400−1×18×10=200−180=20 J\begin{aligned}& =\frac{1}{2} \mathrm{mv}^2-\mathrm{mgh}\\ & =\frac{1}{2} \times1 \times400-1 \times18 \times10 \\ & =200-180=20 \mathrm{~J} \end{aligned}$$
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