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A bob is pulled side way so that string becomes parallel to horizontal and released. Length of the pendulum is 2 m. If due to air resistance loss of energy is 10%, what is the speed with which the bob arrived at the lowest point.

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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 

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