A stone is thrown vertically upward from the top of a tower of height 24.5m with an initial velocity of 19.6 m/s. Calculate :-
Answers
Step-by-step explanation:
Explanation:
When the stone is thrown vertically upwards,
u
= initial velocity =
20
m/s
It will reach some height where its final velocity will become zero,
v
=
0
m/s
a
=
−
g
=
−
10
m
s
−
2
----negative as it is going in direction against the gravitational pull. (Consider
g
=
10
m
s
2
for ease of calculation).
Height = distance it travels upwards will be :
s
=
v
2
−
u
2
2
a
s
=
0
−
20
2
−
2
×
10
m
s
=
−
400
−
20
m
s
=
20
m
Time taken to reach this distance will be :
t
=
v
−
u
a
t
=
0
−
20
−
10
=
2
t
=
2
seconds ----------let this be
t
1
So it reaches
20
m from the peak of tower of height
25
m. So to reach to ground,the stone has to cover:
s
=
20
+
25
=
45
m.
When it starts falling from
45
m above ground, its initial velocity is zero, so:
u
=
0
We know it will come down with uniform acceleration
a
=
g
=
10
m
s
−
2
We know :
s
=
u
t
+
1
2
a
t
2
45
=
0
×
t
+
1
2
×
10
×
t
2
45
×
2
10
=
t
2
45
9
×
2
10
2
=
t
2
9
×
2
2
=
t
2
∴
t
2
=
9
, i.e.
t
=
3
seconds-----Let this be
t
2
Total time taken after throwing the stone upwards will be :
t
=
t
1
+
t
2
t
=
2
+
3
=
5
seconds
∴
The stone will