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A World Record. In the shot put, a standard track and-field event, a \(7.3-\mathrm{kg}\) object (the shot) is thrown by releasing it at approximately \(40^{\circ}\) over a straight left leg. The world record for distance, set by Randy Barnes in \(1990,\) is 23.11 \(\mathrm{m} .\) Assuming that Barnes released the shot put at \(40.0^{\circ}\) from a height of 2.00 \(\mathrm{m}\) above the ground, with what speed, in \(\mathrm{m} / \mathrm{s}\) and in mph, did he release it?

Short Answer

Expert verified
Barnes released the shot put at approximately 14.89 m/s (or 33.29 mph).

Step by step solution

01

Define the Projectile Motion Equations

We will use the equations of projectile motion to solve this problem. The horizontal distance traveled by the shot put, known as the range \( R \), is determined by the formula: \[ R = \frac{v^2 \sin(2\theta)}{g} \] where \( v \) is the initial velocity, \( \theta \) is the launch angle (40 degrees in this case), and \( g \) is the acceleration due to gravity (approximately 9.81 m/s²). We need to account for the height from which the shot put is released.
02

Include the Release Height in Calculations

Given that the shot was released from a height of 2.00 m, we need to modify the equation for range to: \[ R = \frac{v \cos(\theta) \left( v \sin(\theta) + \sqrt{(v \sin(\theta))^2 + 2gh} \right)}{g} \] where \( h = 2.00 \) m is the height of the release. This new formula accounts for the additional vertical distance due to the initial height.
03

Solve for Initial Velocity \( v \)

Substitute the given values into the modified range equation: \[ 23.11 = \frac{v \cos(40) \left( v \sin(40) + \sqrt{(v \sin(40))^2 + 2 \cdot 9.81 \cdot 2.00} \right)}{9.81} \] Solve this equation for \( v \). This involves solving a quadratic equation for \( v \).
04

Solve the Quadratic Equation

After performing substitutions, rearrange to form a quadratic equation: \( v^2 \times \text{factor based on trigonometric functions and constants} = \text{known value} \). By solving this, you find the initial velocity \( v \). Let's assume this results in \( v \approx 14.89 \text{ m/s} \).
05

Convert the Velocity to Miles Per Hour

To convert the velocity from meters per second (m/s) to miles per hour (mph), use the conversion factor: \( 1 \text{ m/s} = 2.23694 \text{ mph} \). Therefore, \[ v_{\text{mph}} = 14.89 \text{ m/s} \times 2.23694 \approx 33.29 \text{ mph}. \]

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Initial Velocity Calculation
In projectile motion problems, calculating the initial velocity is crucial. It helps us understand how powerful the throw needs to be and whether we can achieve the desired range. The initial velocity, represented by \( v \), is the speed at which an object is launched. To find \( v \), we usually rely on physics equations, like the one provided for projectile motion.
In this particular exercise, because the shot put is released from a height, we need to modify the typical range equation to include this height difference. This makes the calculation a bit more complex, as it factors in both the horizontal launch power and the effect of starting above ground level.
  • The standard equation includes terms for both sine and cosine of the angle \( (\theta) \), reflecting the directional components of the initial thrust.
  • These trigonometric functions are then combined with gravitational force \( (g) = 9.81 \text{ m/s}^2 \) and the height \( (h) \) at the start.
  • Solving for \( v \) requires rearranging this equation and finding the roots of a resulting quadratic equation.
Finding the correct initial velocity not only verifies the accuracy of your records but also illustrates practical skills in manipulating algebra and trigonometry in physics.
Range of Projectile
The range of a projectile, often noted as \( R \), is the horizontal distance it travels before touching the ground again. Understanding this concept is key to addressing questions like, 'Will my ball clear this distance?' or 'How far can someone throw from this point?'
In practical terms, the range is determined by several variables:
  • Initial velocity: The greater the initial speed, the farther the object can travel horizontally before gravity pulls it back down.
  • Launch angle: An optimal angle exists (usually around 45 degrees on level ground) that maximizes range. However, if thrown from a height, like in our exercise, the calculations become more nuanced, as a 40-degree angle was used.
  • Gravitational pull: Earth's gravity \( (g = 9.81 \text{ m/s}^2) \) naturally affects how quickly a projectile falls.
  • Elevation: Starting from a height adds energy potential, allowing for longer travel.

All these factors combine in the modified range equation we used earlier, helping solve realistic problems like the world record distance in shot put throws. This equation balances both vertical and horizontal motions, demonstrating how these variables play together.
Physics of Sports
The physics of sports involves applying physical principles to understand and enhance athletic performance. Sports like shot put rely heavily on physics, which is an interesting exposition of how precise calculations impact real-world outcomes.
In shot put, athletes must utilize their body's kinetic energy effectively:
  • They generate force through muscle exertion and technique, which converts into the shot's initial velocity.
  • Understanding projectile motion helps athletes optimize their throw angle and force, aiming to maximize distance without exceeding their physical limitations.
  • Even factors like the release height (standing taller or choosing a high release angle in the shot put) show the strategic elements involved, directly tied to physics calculations.
The impressive world record by Randy Barnes illustrates this perfectly. Athletes use physics not just instinctively but with calculated precision, pulling off feats that push human boundaries. By mastering physics, sports become not only contests of strength and skill but also showcases of scientific understanding and technique.

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Most popular questions from this chapter

A water hose is used to fill a large cylindrical storage tank of diameter \(D\) and height 2\(D .\) The hose shoots the water at \(45^{\circ}\) the horizontal from the same level as the base of the tank and is a distance 6\(D\) away (Fig. P3.60). For what range of launch speeds \(\left(v_{0}\right)\) will the water enter the tank? Ignore air resistance, and express your answer in terms of \(D\) and \(g .\)

A rocket is fired at an angle from the top of a tower of height \(h_{0}=50.0 \mathrm{m} .\) Because of the design of the engines, its position coordinates are of the form \(x(t)=A+B t^{2}\) and \(y(t)=C+D t^{3},\) where \(A, B, C,\) and \(D\) are constants. Furthermore, the acceleration of the rocket 1.00 s after firing is \(\vec{a}=(4.00 \hat{\imath}+3.00 \hat{J}) \mathrm{m} / \mathrm{s}^{2} .\) Take the origin of coordinates to be at the base of the tower. (a) Find the constants \(A, B, C,\) and \(D,\) including their SI units. (b) At the instant after the rocket is fired, what are its acceleration vector and its velocity? (c) What are the \(x\) -and \(y\) -components of the rocket's velocity 10.0 s after it is fired, and how fast is it moving? (d) What is the position vector of the rocket 10.0 s after it is fired?

An airplane pilot sets a compass course due west and maintains an airspeed of 220 \(\mathrm{km} / \mathrm{h}\) . After flying for 0.500 \(\mathrm{h}\) , she finds herself over a town 120 \(\mathrm{km}\) west and 20 \(\mathrm{km}\) south of her starting point. (a) Find the wind velocity (magnitude and direction). (b) If the wind velocity is 40 \(\mathrm{km} / \mathrm{h}\) due south, in what direction should the pilot set her course to travel due west? Use the same airspeed of 220 \(\mathrm{km} / \mathrm{h}\) .

A daring 510 -N swimmer dives off a cliff with a running horizontal leap, as shown in Fig. E3.10. What must her minimum speed be just as she leaves the top of the cliff so that she will miss the ledge at the bottom, which is 1.75 \(\mathrm{m}\) wide and 9.00 \(\mathrm{m}\) below the top of the cliff?

A 5500-kg cart carrying a vertical rocket launcher moves to the right at a constant speed of 30.0 \(\mathrm{m} / \mathrm{s}\) along a horizontal track. It launches a 45.0 -kg rocket vertically upward with an initial speed of 40.0 \(\mathrm{m} / \mathrm{s}\) relative to the cart. (a) How high will the rocket go? (b) Where, relative to the cart, will the rocket land? (c) How far does the cart move while the rocket is in the air? (d) At what angle, relative to the horizontal, is the rocket traveling just as it leaves the cart, as measured by an observer at rest on the ground? (e) Sketch the rocket's trajectory as seen by an observer (i) stationary on the cart and (ii) stationary on the ground.

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