Achild with a weight of 110 n swings on a playground swing attached to 2.00 m long chains. what is the gravitational potential energy (in j) of the child-earth system relative to the child's lowest position at the following times?

Answer

given,

Weight of the child = 110 N

length of the swing,L = 2 m

now, calculating the potential energy when the string is horizontal

  Potential energy = m g h

 now, h = L (1 - cos θ)   where θ is the angle made by the string with the vertical.

     PE = m g L (1 - cos θ)

   when rope is horizontal θ = 90°

     PE = 110 x 2 (1 - cos 90°)

    PE = 220 J

now, calculating potential energy when string made 25° with horizontal

PE = m g L (1 - cos θ)

   when rope is horizontal θ = 25°

     PE = 110 x 2 (1 - cos 25°)

     PE = 20.61 J

does anyone know or what?