In an imaginary atmosphere, the air exerts a small force F on any particle in the direction of the particle’s motion. A particle of mass m projected upward takes a time t1 in reaching the maximum height and t2 in the return journey to the original point. Then

When the particle moves in the upward direction the net acceleration is (g-a) which decreases the net force on the particle and the particle is able to move for larger time while moving downward the net acceleration increases (g+a) and the particle reaches ground faster. Thus, .

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