Question

In lecture, we learned that, if air resistance can be neglected, t up= t down on level ground. That is, an object thrown upwards will take the same amount of time to get up to the top of its flight as to fall back down (to the same height it was thrown from). I this true if air resistance is not negligible? if not, which is larger? Explain.

Answer 1

Time of ascent is equal to time of descent only if resistance of air is not taken into account.

If resistance of air is taken into account then the speed of object on return to ground (descent) will be less than the initial speed with which it was launched vertically upwards.

Therefore, the time taken to go up(ascent) will be less as compared to time taken to come down(descent).

Note: The above phenomenon happens because a part of kinetic energy is used up in overcoming the friction due to air.

Note: Because of resistance due to air the magnitude of velocity momentum and kinetic energy is also less for descent as compared to that of ascent.