UEFA Champions League Quarter Final. Anfield. Liverpool vs Manchester City. 89th minute. Liverpool corner.
Jordan Henderson is taking the corner on the football pitch at Anfield, with dimensions shown above. Manchester City have cloned Vincent Kompany ( tall), all around the penalty area as shown in blue. Mohamed Salah ( tall) is standing on the penalty spot as shown in red.
Henderson wants to kick the ball to deliver the perfect cross to Salah for him to score a goal (and avoiding any blocks by Kompany). What is the least possible angle of elevation (to the nearest degree) above the horizontal pitch surface needed?
Details and assumptions:
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The height of the ball above a point on the ground x m from the corner is given by f ( x ; a ) = − a x 2 + tan ( θ ) x where a > 0 is some parameter and θ is the angle of elevation of the pitch.
Along the line segment from the corner to the penalty spot, we find that it is 1 1 2 + 3 4 2 = 1 2 7 7 m to the penalty spot and [by similar triangles] 3 4 1 4 1 2 7 7 = 1 7 7 1 2 7 7 m to the edge of the penalty area. Therefore, in order to make it over Kompany and to Salah, we must have f ( 1 2 7 7 ; a ) ≤ 1 . 7 5 , f ( 1 7 7 1 2 7 7 ; a ) ≥ 1 . 9 3
In order to make the following steps easier, we will uniformly scale everything by a factor of 1 2 7 7 1 7 . This changes a > 0 to some other A > 0 , but it doesn't change tan θ . The result is f ( 1 7 ; A ) ≤ 1 2 7 7 1 7 ⋅ 1 . 7 5 , f ( 7 ; A ) ≥ 1 2 7 7 1 7 ⋅ 1 . 9 3 and by writing these out: − 1 7 2 A + 1 7 tan θ ≤ 1 2 7 7 1 7 ⋅ 1 . 7 5 ⟹ − 1 7 A + tan θ ≤ 1 2 7 7 1 . 7 5 − 4 9 A + 7 tan θ ≥ 1 2 7 7 1 7 ⋅ 1 . 9 3 Multiplying the first inequality by − 4 9 and the second by 1 7 gives 8 3 3 A + − 4 9 tan θ ≥ 1 2 7 7 − 4 9 ⋅ 1 . 7 5 − 8 3 3 A + 1 1 9 tan θ ≥ 1 2 7 7 2 8 9 ⋅ 1 . 9 3 Adding them: 7 0 tan θ ≥ 1 2 7 7 2 8 9 ⋅ 1 . 9 3 − 4 9 ⋅ 1 . 7 5 and then solving for θ : θ ≥ tan − 1 ( 7 0 1 2 7 7 2 8 9 ⋅ 1 . 9 3 − 4 9 ⋅ 1 . 7 5 ) ≈ 1 0 . 6 9 ∘
Rounded to the nearest degree, this gives an answer of 1 1 .