Math Problem Statement

A baseball thrown at an angle of 65.0 ∘ above the horizontal strikes a building 18.0 m away at a point 5.00 m above the point from which it is thrown. Ignore air resistance. Find the magnitude of the velocity of the baseball just before it strikes the building.

Solution

To solve this problem, we need to use the principles of projectile motion. The steps involved are as follows:

Step 1: Break down the problem

Given:

  • Angle of projection, θ=65.0\theta = 65.0^\circ
  • Horizontal distance (range), R=18.0mR = 18.0 \, \text{m}
  • Vertical displacement, Δy=5.00m\Delta y = 5.00 \, \text{m}

We need to find the magnitude of the velocity of the baseball just before it strikes the building.

Step 2: Horizontal and vertical components of initial velocity

The initial velocity can be broken into horizontal (v0xv_{0x}) and vertical (v0yv_{0y}) components: v0x=v0cosθv_{0x} = v_0 \cos\theta v0y=v0sinθv_{0y} = v_0 \sin\theta where v0v_0 is the initial velocity of the baseball.

Step 3: Time of flight

The time of flight can be determined using the horizontal motion equation: R=v0x×tR = v_{0x} \times t Substituting v0xv_{0x}: t=Rv0cosθt = \frac{R}{v_0 \cos\theta}

Step 4: Vertical displacement equation

Using the vertical motion equation: Δy=v0y×t12gt2\Delta y = v_{0y} \times t - \frac{1}{2} g t^2 where gg is the acceleration due to gravity (9.8m/s29.8 \, \text{m/s}^2).

Substituting tt and the expressions for v0xv_{0x} and v0yv_{0y}: Δy=v0sinθ×Rv0cosθ12g(Rv0cosθ)2\Delta y = v_0 \sin\theta \times \frac{R}{v_0 \cos\theta} - \frac{1}{2} g \left(\frac{R}{v_0 \cos\theta}\right)^2 Simplifying this: Δy=RtanθgR22v02cos2θ\Delta y = R \tan\theta - \frac{g R^2}{2 v_0^2 \cos^2\theta} Solving this equation for v0v_0: v02=gR22cos2θ(RtanθΔy)v_0^2 = \frac{g R^2}{2 \cos^2\theta (R \tan\theta - \Delta y)}

Step 5: Final velocity before impact

The magnitude of the final velocity just before impact can be found using: vf=vfx2+vfy2v_f = \sqrt{v_{fx}^2 + v_{fy}^2} where

  • vfx=v0x=v0cosθv_{fx} = v_{0x} = v_0 \cos\theta (since horizontal velocity remains constant)
  • vfy=v0ygtv_{fy} = v_{0y} - gt

First, solve for v0v_0, then calculate vfxv_{fx} and vfyv_{fy}, and finally, find vfv_f.

Let's calculate these step by step.

Calculation

  1. Calculate v0v_0:

v02=(9.8)(18.0)22cos2(65.0)(18.0tan(65.0)5.00)v_0^2 = \frac{(9.8)(18.0)^2}{2 \cos^2(65.0^\circ) \left(18.0 \tan(65.0^\circ) - 5.00\right)}

  1. Calculate vfxv_{fx} and vfyv_{fy}:

vfx=v0cos(65.0)v_{fx} = v_0 \cos(65.0^\circ)

vfy=v0sin(65.0)g×tv_{fy} = v_0 \sin(65.0^\circ) - g \times t

  1. Calculate vfv_f:

vf=vfx2+vfy2v_f = \sqrt{v_{fx}^2 + v_{fy}^2}

Now, I'll compute the numerical values.The magnitude of the velocity of the baseball just before it strikes the building is approximately 12.91 m/s.

Would you like to go into further detail or have any questions about the steps? Here are 5 related questions to consider:

  1. How would the result change if the angle of projection was different?
  2. What if the initial speed of the baseball was known—how could we find the time of flight?
  3. How does air resistance impact the velocity in real-world scenarios?
  4. What would be the time of flight for this problem?
  5. How would the maximum height reached by the baseball be calculated?

Tip: When dealing with projectile motion, always start by breaking down the motion into horizontal and vertical components, as it simplifies the calculations.

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Math Problem Analysis

Mathematical Concepts

Projectile Motion
Kinematics
Trigonometry

Formulas

Horizontal component of initial velocity: v_{0x} = v_0 \cos\theta
Vertical component of initial velocity: v_{0y} = v_0 \sin\theta
Time of flight: t = \frac{R}{v_0 \cos\theta}
Vertical displacement: \Delta y = v_{0y} \times t - \frac{1}{2} g t^2
Final velocity: v_f = \sqrt{v_{fx}^2 + v_{fy}^2}

Theorems

Equations of Motion

Suitable Grade Level

Grades 11-12