HCV! In an imaginary atmosphere the air exerts a force F on any particle in the direction of the particle’s motion. A particle of mass m projected upward takesa time t1 in reaching maximum height and t2 in the return to the original point. Then\tt1\tt1>t2.\tt1=t2.\trelation between t1 and t2 depends on the mass of the particle

Dear Student

 

While going up the net downward acceleration is (g-a) thus decreasing the g_effective  and hence increasing the time of upward motion while coming down the force and g both act downward thus increasing the g_effective (say g+a) thus decreasing the time of downward journey than usual.

 

Hence t₁ > t₂

mrs shashi k sharma,i am a student of +2 and have the same doubt but contrary to your answer, there is no mention of a gravitational force in the question there is only an imaginary atmosphere. 

 

 

Yes there is an imaginary atomsphere present.but it is also given that air exert a small force on any particle in the direction of particle's motion.we know that a particle or any object can move in only one particular direction at any instant on time.now towards the question.when a particle moves from an initial position,it is acted upon by a force due to air,now when the same particle returns to that same position,it means a force is definitely acting in the direction to make the particle reach at its initial point,from where it was started...hope doubt is clear now.