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Work Energy and Power question

2009 · Q157
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Work Energy and Power question

2009 · Q157

NEETPhysicsWork Energy and PowerMCQ+4 / −1
A body of mass 1 kg is thrown upwards with a velocity 20 m/s. It momentarily comes to rest after attaining a height of 18 m. How much energy is lost due to air friction? (g = 10 m/s2)
  1. A
    30 J
  2. B
    40 J
  3. C
    10 J
  4. D
    20 J
View written solutionFree

Correct answer: D

Initial velocity u = 20 m/s; m = 1 kg

Kinetic energy = maximum potential energy

Initial kinetic energy = 12×1×202=200 J{1 \over 2} \times 1 \times {20^2} = 200\,J21​×1×202=200J

Mgh (max) = 200 J

∴\therefore∴ h = 20 m

The height travelled by the body, h' = 18 m

∴\therefore∴ Loss of energy due to air friction = mgh – mgh'

⇒\Rightarrow⇒ Energy lost = 200 J – 1 × 10 × 18 J = 20 J.

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