1) Measurement of time depends on the reaction time of the human measuring the time / operating the stop clock. There will always be error in measuiring the time whereas measuring the distance is limited by the least count of the measuring device. Hence distance / displacement measurement yeilds better results compared to experiment invlving measurement of time. 2) Frictional force generated by Air also called drag force which is proportional to the speed and opposes the motion of the projectile introduces error in the experiment. Solution 1) Measurement of time depends on the reaction time of the human measuring the time / operating the stop clock. There will always be error in measuiring the time whereas measuring the distance is limited by the least count of the measuring device. Hence distance / displacement measurement yeilds better results compared to experiment invlving measurement of time. 2) Frictional force generated by Air also called drag force which is proportional to the speed and opposes the motion of the projectile introduces error in the experiment..