A body of mass 1 kg is thrown upwards with a velocity of 20 m/s. It momentarily comes to rest after attaining a height of 18 m. How much energy is lost due to air friction? [Take g = 10 m/s²]
Friction is a force that opposes the relative motion between two surfaces in contact. It arises due to microscopic irregularities and adhesive interactions. There are two main types of friction: static friction which prevents motion and kinetic friction which acts during motion. Friction is essential for everyday activities like walking and driving.
Class 11 Physics Chapter 5 Work, Energy and Power discusses the concepts of work, energy and power focusing on their definitions and relationships. It covers the types of energy such as kinetic and potential and explores the principle of conservation of energy providing examples and applications relevant for CBSE EXAM 2024-25.
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NCERT Solutions for Class 11 Physics Chapter 5 Work, Energy and Power
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To find the energy lost due to air friction, we first calculate the initial kinetic energy and the potential energy at the maximum height.
1. Initial kinetic energy (K.E.) when the body is thrown:
K.E. = (1/2) * m * v²
K.E. = (1/2) * 1 kg * (20 m/s)²
K.E. = (1/2) * 1 * 400
K.E. = 200 J.
2. Potential energy (P.E.) at the maximum height (h = 18 m):
P.E. = m * g * h
P.E. = 1 kg * 10 m/s² * 18 m
P.E. = 180 J.
3. The energy lost to air friction is given by the difference between the initial kinetic energy and the potential energy at the maximum height:
Energy lost = K.E at the start – P.E.
Energy lost = 200 J – 180 J
Energy lost = 20 J.