Math Problem Statement

a shot after leaving a gun passes just over a wall of a fort horizontally. If the wall is 64 ft. high and is 192 ft away from the gun. find the direction and the velocity of projection of the shot

Solution

This is a problem of projectile motion where a shot passes just over a wall at a known height and horizontal distance. To solve this, we need to find the initial velocity (v0v_0) and the angle of projection (θ\theta).

Known Values

  • Height of the wall (hh) = 64 ft
  • Horizontal distance to the wall (xx) = 192 ft
  • Acceleration due to gravity (gg) = 32 ft/s² (standard value in feet).

Equations of Motion

  1. Horizontal motion: x=v0cosθtx = v_0 \cos\theta \cdot t t=xv0cosθt = \frac{x}{v_0 \cos\theta}

  2. Vertical motion: y=v0sinθt12gt2y = v_0 \sin\theta \cdot t - \frac{1}{2} g t^2 At x=192ftx = 192 \, \text{ft}, y=64fty = 64 \, \text{ft}.

Step 1: Substitute tt from Horizontal Motion into Vertical Motion

y=v0sinθxv0cosθ12g(xv0cosθ)2y = v_0 \sin\theta \cdot \frac{x}{v_0 \cos\theta} - \frac{1}{2} g \left( \frac{x}{v_0 \cos\theta} \right)^2 Simplify: y=xtanθgx22v02cos2θy = x \tan\theta - \frac{g x^2}{2 v_0^2 \cos^2\theta} Substitute x=192x = 192, y=64y = 64, and g=32g = 32: 64=192tanθ3219222v02cos2θ64 = 192 \tan\theta - \frac{32 \cdot 192^2}{2 v_0^2 \cos^2\theta}

Step 2: Solve for v02v_0^2 and tanθ\tan\theta

Rewrite the equation: 64=192tanθ3219222v02(1+tan2θ)64 = 192 \tan\theta - \frac{32 \cdot 192^2}{2 v_0^2 (1 + \tan^2\theta)} Let k=tanθk = \tan\theta, so 1+k2=sec2θ1 + k^2 = \sec^2\theta. Rearrange: 64=192k3219222v02(1+k2)64 = 192 k - \frac{32 \cdot 192^2}{2 v_0^2 (1 + k^2)} 64(1+k2)=192k(1+k2)3219222v0264 (1 + k^2) = 192 k (1 + k^2) - \frac{32 \cdot 192^2}{2 v_0^2} This equation involves both v0v_0 and θ\theta, so we solve numerically or iteratively for practical values.

Would you like me to proceed with the numerical solution or provide a symbolic simplification? Let me know!


Expanding Understanding:

  1. What is the effect of increasing the height of the wall on the angle of projection?
  2. How does the horizontal distance influence the initial velocity?
  3. Can we solve this problem if gravity is different (e.g., on the Moon)?
  4. What happens if the shot must clear another obstacle beyond the wall?
  5. How can air resistance affect the trajectory?

Tip: For projectile motion, always separate horizontal and vertical components to simplify equations.

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Math Problem Analysis

Mathematical Concepts

Projectile Motion
Kinematics
Trigonometry
Algebra

Formulas

x = v_0 cos(θ) * t
y = v_0 sin(θ) * t - 1/2 * g * t^2
y = x * tan(θ) - (g * x^2) / (2 * v_0^2 * cos^2(θ))

Theorems

Projectile Motion Equations
Trigonometric Identities

Suitable Grade Level

Grades 10-12