a boll is projected from ground at an angle 60 degree with horizontal and with initial velocity of 20 m/s. Calculate the time when the angle between velocity vector and acceleration due to gravity is 135 degree...?
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Answers
Explanation:
Final Answer : H = 125 (2-√3)m
|u| = 50(√3-1) m/s .
Steps and Understanding:
1) Let the initial velocity of projectile be u m/s at an angle of 30° from horizontal on top of a tower of height H.
For figure see pic.
2) Given,
Initial velocity, u = u (say)
Height of tower, h = H
Projection angle,theta = 30°
Fall at angle 45° with the horizontal on ground.
a(y) = -10m/s^2 (g)
a(x) = 0
time taken to reach ground, t = 5s
Vertical upward direction is +.
and vice versa.
3) Vertical Equation of motion,
4)
5) Since, v(y) is negative as v(y) is in downward direction, so
Since, F(x) =0
so, velocity along horizontal direction will be constant.
v(x) = u cos(30°)
And looking at pic,
6) Using u in equation (1) ,
Therefore,
speed of projection u = 50(√3-1)m/s
Height of tower, H = 125(2-√3)m
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H - 125(2-√3)
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