Question 421812

  Denote the length of the arc L=50 cm and the angle {{{ theta=2.5}}}.

  As we know {{{L=r*(theta)}}}, where r is the length of the pendulum.

   {{{r=L/(theta)}}}

   {{{r=50/2.5}}}
  
    {r=20}

  Answer: the length of pendulum is 20 cm.