a stone is projected from the top of a cliff 20m high. how long does it strike the ground? If the line joining the point of projection to the point where it hits the ground makes an angle of 30 degree with the horizontal, caluculate the velocity of the stone
Answers
Answer:
Height of the cliff h
1
=20m
Velocity of projectile V=30m/s
Initial upward velocity v
y
=Vsinθ=30×sin30
∘
=15m/s.
Horizontal velocity, v
x
=Vcosθ=30cos30
o
m/s
Time taken to reach maximum height, t
1
=
g
V
y
=
10
15
=1.5sec.
Height above the cliff h
2
=
2g
v
y
2
=
2×10
15
2
=11.25m
Therefore, the maximum height, h
max
=h
1
+h
2
=20+11.25=31.25m.
Time taken to free fall from max height, t
2
=
g
2h
max
=
g
2×31.25
=2.5sec.
Thus, the total time taken during the entire flight t
total
=t
1
+t
2
=1.5+2.5=4sec
Total horizontal distance covered R=v
x
t
total
=30×cos30
∘
×4=60
3
Answer:
we have
v=?
u=0m/s
h=20m
g=10m/s (approx)
so,
v²=u²+2gh
v²=(0)²+2×10×20
v²=0+400
v²=400
v=root 400
v=20m/s
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