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```
Sir, i am a student of class 9 and i have a doubt. The question is.. From the top of a tower of 200m height, a stone is projected vertically upwards with a velocity of 49 m/s. Calculate the time to reach the ground. I Did approach the answer through a website .. but i dint understand why the initial velocity (u) was with a negative sign. Sir.. can u show me the method and the explanations of my doubts,.. Please

```
8 years ago

Kurma Anudeep
30 Points
```							let s=200m
u=-49m/s
a=9.8m/s^2
v^2=u^2+2as
=2401+19.6*200
=2401+3920
v=79.5m/s
v=u+at
79.5=-49+9.8t
128.5=9.8t
t=128.5/9.8=13.11s
u is negative because the ball is thrown against the gravitational force
ALL THE BEST
```
8 years ago
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