Class 9
Chapter 9 Class 9 - Force and Laws Of Motion

Two persons manage to push a motorcar of mass 1200 kg at a uniform velocity along a level road. The same motorcar can be pushed by three persons to produce an acceleration of 0.2 m s−2. With what force does each person push the motorcar? (Assume that all persons push the motorcar with the same muscular effort.)



If 2 people push


Then car moves with uniform velocity

So, Acceleration = 0

That means

  Total Force on Body is balanced


  Force by 2 People = Force of Friction

  2F = Force of Friction

  Force of Friction = 2F


If 3 people push


Then car moves with Acceleration = 0.02 m/s2

Net Force = Force of 3 people – Force of Friction

    = 3F – 2F

    = F



So, let’s find F


  Mass of motor car = m = 1200 kg

  Acceleration = a = 0.2 m/s2

  Force = F



  Force = Mass × Acceleration

  F = 1200 × 0.2

  F = 1200 × 2/10

  F = 120 × 2

  F = 240N

Thus, each person pushes the motorcar by 240  force 

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CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo