Given,

Potential energy of pendulum is converted into kinetic energy and lost energy in air.

So, PE = KE + lost energy......................(1)

According to question, lost energy = 10% of

PE =0.1PE Eqn (1) becomes

PE = KE + 0.1PE

=> 0.9PE = KE

=>0.9 mgh = 0.5 mv

=> 0.9 gh = 0.5 v

=> v = 1.8gh v = speed at the lowest point.

h = length of pendulum = 2m g

= 9.81 m/s Plug in the values of g and h

v = 5.94 m/s