Question
sir i had asked a ques and its ans was also replied by you, but still i have a doubt that in 1st part you take g as -ve because motion is against gravity and it is clear to me but in 2nd why g is taken as -ve? here, the motion is not against gravity, so plz tell me the concept of g? wten it is -ve or +ve.
b) in second part we have to calculate the time of journey from top of 25 m high building to ground.
for this we should use
h = -ut + gt2/2 [in this case we are using upward direction as - ve and downward as + ve]
so 25 = -20t + 10t2/2
or 5t2 - 20t - 25 = 0
or t2- 4t - 5 = 0
or (t+1)(t-5) = 0
or t = 5 , -1
so t = 5 sec.
This is answer of the same problem but here i am using g +ve, I want to say only that it will always be your opinion to consider the sign of direction. You can consider any of the direction as positive and negative.