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