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Concepts Of Physics MCQ Edition [Volume 1]
Exam
Concepts Of Physics MCQ Edition [Volume 1]
Subject
Physics
Chapter
Rest and Motion Kinematics

Concepts Of Physics MCQ Edition [Volume 1] · Physics · Rest and Motion Kinematics

During a soccer practice session, the football is positioned at the...

During a soccer practice session, the football is positioned at the centre of the field 4040 yards from the 10 ft10 \text{ ft} high goalposts. A goal is attempted by kicking the football at a speed of 64 ft/s64 \text{ ft/s} at an angle of 45^{}^{{}^{\circ}} to the horizontal. Will the ball reach the goal post?

Options

  1. AYes, it reaches the goalposts at a height of 9.5 ft9.5 \text{ ft}.
  2. BNo, it passes over the goalposts at a height of 12.5 ft12.5 \text{ ft}.
  3. CYes, it reaches the goalposts at a height of 7.5 ft7.5 \text{ ft}.
  4. DNo, it lands on the ground before reaching the goalposts.

Correct answer

C. Yes, it reaches the goalposts at a height of 7.5 ft7.5 \text{ ft}.

Step-by-step solution

Given, initial speed u=64 ft/su = 64 \text{ ft/s}

Angle of projection \theta = 45^{}^{{}^{\circ}}

Horizontal distance to goalposts x=40 yards=40×3=120 ftx = 40 \text{ yards} = 40 \times 3 = 120 \text{ ft}

Acceleration due to gravity g=32 ft/s2g = 32 \text{ ft/s}^2

The equation of trajectory is given by:

y=xtan⁡θ−gx22u2cos⁡2θy = x \tan \theta - \dfrac{g x^2}{2 u^2 \cos^2 \theta}

Substituting the values:

y = 120 \tan 45^{}^{{}^{\circ}} - \dfrac{32 \times (120)^2}{2 \times (64)^2 \cos^2 45^{}^{{}^{\circ}}}

y=120(1)−32×144002×4096×12y = 120 (1) - \dfrac{32 \times 14400}{2 \times 4096 \times \dfrac{1}{2}}

y=120−14400128y = 120 - \dfrac{14400}{128}

y=120−112.5=7.5 fty = 120 - 112.5 = 7.5 \text{ ft}

Since the height of the ball is 7.5 ft7.5 \text{ ft}, which is less than the goalpost height of 10 ft10 \text{ ft}, the ball reaches the goalposts at a height of 7.5 ft7.5 \text{ ft}.
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