1.

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.

Answer»

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 



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