Question

From the top of a tower, 28 m high, a stone is thrown vertically up with a velocity of 9m/s. After how much time will the stone reach the ground? With what velocity does it strike the ground?

Answer 1

v = 0m/s g=9.812 m/s²

From A to B,
u=9m/s; v=0m/s; a=-g=-9.812m/s²

v = u + at₁

0 = 9 + (-9.812 x t₁)
t₁ = 0.917 sec
Now, v² = u² + 2(-g)x

x =4.128 m

From B to C,
u=0m/s g=9.912m/s² s=x+28=32.128m
v²=u²+2gs
v=`sqrt(2 xx 9.812 xx  32.128)` = 25.11m/s
v=u+gt²
`t<sub>2</sub> =v/g` 
t₂ = 2.559 sec
Total time = t₁ + t₂
Total time = 0.917 + 2.559 = 3.476 sec

The stone will strike the ground after 3.476 sec at a velocity of 25.11 m/s