Math Problem Statement

At what initial speed must the basketball player in the figure throw the ball, at angle θ₀ = 45° above the horizontal, to make the foul shot? The horizontal distances are d₁ = 1.0 ft and d₂ = 14 ft, and the heights are h₁ = 7.8 ft and h₂ = 10 ft.

Solution

To solve this problem, we need to find the initial speed v0v_0 at which the basketball player must throw the ball at an angle of θ0=45\theta_0 = 45^\circ to successfully make the shot.

Given dataTo solve this problem, we need to find the initial speed v0v_0 at which the basketball player must throw the ball at an angle of θ0=45\theta_0 = 45^\circ to successfully make the shot.

Given

  • Horizontal distances: d1=1.0ftd_1 = 1.0 \, \text{ft} (initial horizontal distance), d2=14ftd_2 = 14 \, \text{ft} (total horizontal distance).
  • Heights: h1=7.8fth_1 = 7.8 \, \text{ft} (initial height), h2=10fth_2 = 10 \, \text{ft} (final height of the hoop).
  • Angle of projection: θ0=45\theta_0 = 45^\circ.

Step-by-step solution:

  1. Determine the total horizontal distance:
    Total horizontal distance is D=d1+d2=1.0ft+14ft=15.0ftD = d_1 + d_2 = 1.0 \, \text{ft} + 14 \, \text{ft} = 15.0 \, \text{ft}.

  2. Equations of motion: We can use the equations for projectile motion. The horizontal and vertical displacements are described by:

    • Horizontal motion: x(t)=v0cos(θ0)tx(t) = v_0 \cos(\theta_0) t where x(t)=Dx(t) = D is the total horizontal distance, and tt is the time of flight.

    • Vertical motion: y(t)=h1+v0sin(θ0)t12gt2y(t) = h_1 + v_0 \sin(\theta_0) t - \frac{1}{2} g t^2 where y(t)=h2y(t) = h_2 is the final height of the ball, and g=32.2ft/s2g = 32.2 \, \text{ft/s}^2 is the acceleration due to gravity.

  3. Find the time of flight tt: From the horizontal motion equation, solve for tt: t=Dv0cos(θ0)t = \frac{D}{v_0 \cos(\theta_0)} Since θ0=45\theta_0 = 45^\circ, cos(45)=sin(45)=22\cos(45^\circ) = \sin(45^\circ) = \frac{\sqrt{2}}{2}, so this simplifies to: t=Dv022=2Dv02t = \frac{D}{v_0 \cdot \frac{\sqrt{2}}{2}} = \frac{2D}{v_0 \sqrt{2}}

  4. Substitute into the vertical motion equation: Now substitute tt into the vertical motion equation: h2=h1+v0sin(45)t12gt2h_2 = h_1 + v_0 \sin(45^\circ) t - \frac{1}{2} g t^2 Again, sin(45)=22\sin(45^\circ) = \frac{\sqrt{2}}{2}, so: h2=h1+v0222Dv0212g(2Dv02)2h_2 = h_1 + v_0 \cdot \frac{\sqrt{2}}{2} \cdot \frac{2D}{v_0 \sqrt{2}} - \frac{1}{2} g \left(\frac{2D}{v_0 \sqrt{2}}\right)^2 Simplifying: h2=h1+DgD22v02h_2 = h_1 + D - \frac{g D^2}{2 v_0^2}

  5. Solve for v0v_0: Rearranging the equation to solve for v0v_0: v02=gD22(h1+Dh2)v_0^2 = \frac{g D^2}{2 (h_1 + D - h_2)} Substituting the known values: v02=32.2×(15)22(7.8+1510)v_0^2 = \frac{32.2 \times (15)^2}{2 (7.8 + 15 - 10)} Simplifying: v02=32.2×2252(12.8)v_0^2 = \frac{32.2 \times 225}{2 (12.8)} v02=32.2×22525.6v_0^2 = \frac{32.2 \times 225}{25.6} v02282.42v_0^2 \approx 282.42 Taking the square root: v016.81ft/sv_0 \approx 16.81 \, \text{ft/s}

Thus, the initial speed v016.8ft/sv_0 \approx 16.8 \, \text{ft/s}.

Let me know if you would like further clarification, details, or if you have any questions!


Related questions:

  1. How does air resistance affect the trajectory of a projectile?
  2. Can you derive the time of flight for a projectile in general terms?
  3. How would the required initial speed change if the angle was different from 4545^\circ?
  4. What is the optimal angle to achieve the maximum range in projectile motion?
  5. How do we account for the Earth's curvature in long-distance projectile motion?

Tip: Always check units when solving physics problems to ensure consistency across calculations.

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Math Problem Analysis

Mathematical Concepts

Projectile Motion
Kinematics
Trigonometry

Formulas

x(t) = v₀ cos(θ₀) t
y(t) = h₁ + v₀ sin(θ₀) t - (1/2) g t²
v₀² = (g D²) / (2 (h₁ + D - h₂))

Theorems

Equations of Motion
Kinematic Equations

Suitable Grade Level

Grades 10-12