Question

The friction of the air causes vertical retardation equal to one tenth of the acceleration due to gravity (take g = 10ms^-2) the time of flight will be decreased by

(a) 0% 

(b)1% 

(c) 9% 

(d) 11%

Answer 1

Answer is (c) 9%

The time to rise to the top = 91% of u sinθ/g. Also maximum height Hm = 91% of u² sin² θ/2g. And time of fall ≅ using θ/g. 

Hence time of flight is decreased by 9%.