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Question

Two guns situated on the top of a hill of height 15 m fire one shot each with the same speed 5 m/s with some time interval between the firings. One gun fires horizontally and other fires upwards at an angle of 45 with the horizontal. The shots collide in air at point P. Then

A
P(x,y)=p(5,10)
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B
P(x,y)=p(10,5)
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C
Time interval between firings is 0.8 s
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D
Time interval between firings is 0.4 s
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Solution

The correct options are
A P(x,y)=p(5,10)
D Time interval between firings is 0.4 s
Given, speed of shots =5 m/s
Height of hill =15 m
Angle of fire of one shot =45 with horizontal
Angle of fire of other shot =0 with horizontal
We know that, equation of trajectory of projectile is given by, Y=X tanθgX22u2cos2θ
[origin of co- ordinate system for this equation is at point of projection]
For shot 1,
Y=X×110X22×52×12
Y=X2X25(1)
Similarly, of shot 2
Y=X×010X22×52×1
Y=X25(2)
As both shots collide in air at a point P then its x and y co-ordinates should be same.
From (1) and (2)
X2X25=X25
XX25=0
X(1X5)=0
X=0 and X=5 ----(3)
on putting (3) in (2)
Y=5

Therefore wrt original coordinate system with origin at bottom of the tower,
co - ordinates of P is x=5 m and y=10 m

Time taken by shot fired at 45 with horizontal to reach point P, is t1=55cos45=2=1.4 s [Horizontal motion]
Time taken by shot fired at horizontal to reach point P, is t2=55=1 s [Horizontal Motion]
Time internal between firings for collision to happen is =t1t2=1.41=0.4 s

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