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A tacheometer is setup at A and the readings on the staff at B are 1.m, 2.m, 3m and the inclination of line of sight is + 10°. Calculate the vertical distance. Take k = 100, c = 0?
34.00 m
34.202 m
35.202 m
36.202 m
34.202 m
Given: Staff readings = 1.0 m, 2.0 m, 3.0 m, Angle of inclination θ=+10°, Multiplying constant k=100, Additive constant c=0
Staff readings = 1.0 m, 2.0 m, 3.0 m, Angle of inclination θ=+10°, Multiplying constant k=100, Additive constant c=0
V=k⋅S⋅2sin(2θ)+c⋅sin(θ)
Calculate Staff Intercept (S)
The staff intercept S is the difference between the top hair reading (Stop) and the bottom hair reading (Sbottom).
S=Stop−Sbottom=3.0 m−1.0 m=2.0 m
Apply Vertical Distance Formula
For an inclined line of sight, the formula for vertical distance V is V=k⋅S⋅sin(θ)⋅cos(θ)+c⋅sin(θ), which simplifies using trigonometric identity sin(2θ)=2sin(θ)cos(θ).
V=k⋅S⋅2sin(2θ)+c⋅sin(θ)
Substitute Values and Solve
Substitute k=100, S=2.0 m, θ=10°, and c=0 into the formula.
V=100×2.0×2sin(20°)=100×sin(20°)
Final Numerical Calculation
Since sin(20°)≈0.3420201, we multiply by 100 to get the vertical distance.
V=100×0.3420201=34.202 m
B is correct because calculating V=100×2.0×sin(10°)cos(10°) gives exactly 34.202 m.
In tacheometry questions, if the staff is held vertical (standard case), use V=kSsin(θ)cos(θ)+csin(θ). If the staff is normal to the line of sight, the formula changes to V=(kS+c)sin(θ).