Math Problem Statement

A man throws a stone from the top of a building 164 m above the ground. Its initial velocity = 43.3 m/s at an angle 30 degrees. As the stone hits the ground, find x.

Solution

To find the horizontal distance (denoted as xx) that the stone travels before hitting the ground, we need to break down the problem into horizontal and vertical components. This is a projectile motion problem.

Step 1: Decompose the initial velocity into components

The initial velocity (v0=43.3m/sv_0 = 43.3 \, \text{m/s}) is launched at an angle of 3030^\circ.

  • Horizontal velocity (v0xv_{0x}): v0x=v0cos(θ)=43.3cos(30)v_{0x} = v_0 \cos(\theta) = 43.3 \cos(30^\circ) v0x=43.3×32=37.5m/sv_{0x} = 43.3 \times \frac{\sqrt{3}}{2} = 37.5 \, \text{m/s}

  • Vertical velocity (v0yv_{0y}): v0y=v0sin(θ)=43.3sin(30)v_{0y} = v_0 \sin(\theta) = 43.3 \sin(30^\circ) v0y=43.3×12=21.65m/sv_{0y} = 43.3 \times \frac{1}{2} = 21.65 \, \text{m/s}

Step 2: Time of flight

To find the time it takes for the stone to hit the ground, we use the vertical motion. The vertical displacement is y=164my = -164 \, \text{m} (since it falls 164 m from the building top).

Using the kinematic equation for vertical motion: y=v0yt+12at2y = v_{0y} t + \frac{1}{2} a t^2 where:

  • y=164my = -164 \, \text{m}
  • v0y=21.65m/sv_{0y} = 21.65 \, \text{m/s}
  • a=9.8m/s2a = -9.8 \, \text{m/s}^2 (acceleration due to gravity)
  • t=?t = ? (time of flight)

Substitute the known values: 164=21.65t12(9.8)t2-164 = 21.65 t - \frac{1}{2} (9.8) t^2 164=21.65t4.9t2-164 = 21.65 t - 4.9 t^2 Rearranging: 4.9t221.65t164=04.9 t^2 - 21.65 t - 164 = 0

Now, solve this quadratic equation for tt using the quadratic formula: t=b±b24ac2at = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} where a=4.9a = 4.9, b=21.65b = -21.65, and c=164c = -164.

Step 3: Find horizontal distance xx

Once we calculate tt, we can find the horizontal distance using the formula: x=v0xtx = v_{0x} t where v0x=37.5m/sv_{0x} = 37.5 \, \text{m/s} and tt is the time of flight we just found.

Let me calculate the time tt and the distance xx.The time of flight is approximately 8.40seconds8.40 \, \text{seconds}, and the horizontal distance traveled (denoted as xx) is approximately 315.06meters315.06 \, \text{meters}.

Would you like further details or have any questions?

Here are some related questions to consider:

  1. How would changing the launch angle affect the horizontal distance?
  2. What happens if the initial velocity is increased while keeping the same angle?
  3. How would air resistance alter the result compared to the ideal projectile motion calculated here?
  4. Can you calculate the maximum height reached by the stone?
  5. What would the horizontal distance be if the stone was thrown from a lower height?

Tip: In projectile motion, the horizontal velocity remains constant because there is no horizontal acceleration (ignoring air resistance).

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Math Problem Analysis

Mathematical Concepts

Projectile Motion
Kinematic Equations
Trigonometry

Formulas

Horizontal velocity: v_{0x} = v_0 cos(θ)
Vertical velocity: v_{0y} = v_0 sin(θ)
Kinematic equation: y = v_{0y}t + (1/2)at^2
Time of flight: t = [-b ± √(b^2 - 4ac)] / 2a
Horizontal distance: x = v_{0x} * t

Theorems

Pythagorean Theorem
Quadratic Formula

Suitable Grade Level

Grades 11-12