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Work, Energy And Power

Question
CBSEENPH11017256

A spring of force constant 10N/m is lying on a frictionless table with one end fixed and another end attached with 0.1 kg mass. The mass is pushed towards fix end by 8cm and released. Find the velocity of mass when the spring becomes normal.

Solution
Given, 
Spring constant, k = 10 N/m
The potential energy stored in spring when compressed by 8cm is,
straight U space equals 1 half kx squared
space space space equals 1 half 10 cross times left parenthesis 0.08 right parenthesis squared 
  equals 0.032 straight J 
Let, v be the velocity of mass when spring becomes normal.
Applying the law of conservation of energy, we get 
          space space 1 half mv squared equals straight U  
                   straight v space equals square root of fraction numerator 2 straight U over denominator straight m end fraction end root

space space space equals square root of fraction numerator 2 cross times 0.032 over denominator 0.1 end fraction end root

space space space equals 0.8 straight m divided by straight s