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A projectile is being launched from ground level with no air resistance. You want to avoid having it enter a temperature inversion layer in the atmosphere a height \(h\) above the ground. (a) What is the maximum launch speed you could give this projectile if you shot it straight up? Express your answer in terms of \(h\) and \(g .\) (b) Suppose the launcher available shoots projectiles at twice the maximum launch speed you found in part (a). At what maximum angle above the horizontal should you launch the projectile? (c) How far (in terms of \(h\) ) from the launcher does the projectile in part (b) land?

Short Answer

Expert verified
(a) \( v = \sqrt{2gh} \), (b) \( \theta = 30^{\circ} \), (c) Range = \( 4h\sqrt{3} \).

Step by step solution

01

Determine Maximum Launch Speed for Part (a)

To find the maximum launch speed for the projectile shot straight up without exceeding height \( h \), use the energy conservation principle. Initially, the projectile has kinetic energy \( \frac{1}{2}mv^2 \) and at the maximum height \( h \), it has potential energy \( mgh \). Setting these equal gives: \( \frac{1}{2}mv^2 = mgh \). Simplify to find \( v = \sqrt{2gh} \). This is the maximum launch speed for the projectile shot straight up.
02

Calculate the Maximum Angle for Part (b)

Given the speed from the launcher is twice the maximum found in part (a), which is \( v_0 = 2\sqrt{2gh} \). The projectile should not exceed height \( h \), meaning only half the vertical component of this speed can be \( \sqrt{2gh} \), thus \( v_0 \sin(\theta) = \sqrt{2gh} \). Solve for \( \theta \) to get \( \sin(\theta) = \frac{\sqrt{2gh}}{2\sqrt{2gh}} = \frac{1}{2} \), so \( \theta = 30^{\circ} \).
03

Determine the Range for Part (c)

The horizontal range of the projectile is given by \( R = \frac{v_0^2 \sin(2\theta)}{g} \). Substitute \( v_0 = 2\sqrt{2gh} \) and \( \theta = 30^{\circ} \) into the equation: \( R = \frac{(2\sqrt{2gh})^2 \sin(60^{\circ})}{g} \). This simplifies to \( R = \frac{8gh \cdot \frac{\sqrt{3}}{2}}{g} = 4h\sqrt{3} \).

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Key Concepts

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

Kinetic Energy
Kinetic energy is the energy an object possesses due to its motion. In the context of projectile motion, this energy is dependent on the speed and mass of the projectile. The formula for kinetic energy is given by \( KE = \frac{1}{2}mv^2 \), where \( m \) is the mass of the projectile and \( v \) is the velocity.
When the projectile is launched, it starts with maximum kinetic energy, which gradually converts into potential energy as it ascends. In step 1 of the solution, kinetic energy was used to determine the maximum launch speed, using the equation \( \frac{1}{2}mv^2 = mgh \). Understanding kinetic energy helps us determine how fast a projectile needs to move to reach a certain height. This is pivotal in solving problems where the conservation of energy principle applies.
Potential Energy
Potential energy is the stored energy of position possessed by an object. When it comes to projectile motion, potential energy is primarily due to gravitational forces. The formula to determine potential energy at a height \( h \) is \( PE = mgh \), where \( m \) is mass, \( g \) is the acceleration due to gravity, and \( h \) is the height above the ground.
As a projectile climbs upward, its kinetic energy is converted into potential energy. This conversion process continues until it reaches its peak height, where kinetic energy is minimized, and potential energy is maximized. Step 1 in the solution uses potential energy to equate with kinetic energy to find how high a projectile can go based on its initial kinetic energy. This understanding of potential energy is critical in predicting the maximum height achievable during projectile motion.
Launch Angle
The launch angle is the initial angle between the projectile's velocity vector and the horizontal axis. This angle significantly impacts both the maximum height reached and the range covered by the projectile. When an angle is chosen correctly, it ensures that the projectile meets specific conditions, such as avoiding a predefined height.
In the step-by-step solution, they determined the maximum launch angle such that the projectile stays within certain limits. The angle of \( 30^{\circ} \) was found using the relation \( \sin(\theta) = \frac{1}{2} \), ensuring that the projectile does not exceed height \( h \). Understanding and adjusting the launch angle is a crucial aspect of controlling projectile motion effectively.
Energy Conservation
Understanding energy conservation is key to analyzing projectile motion. The law of conservation of energy posits that energy cannot be created or destroyed, only transformed from one form to another. For a projectile, as it moves j through its trajectory, energy shifts between kinetic and potential forms.
This principle is applied in step 1. The equation \( \frac{1}{2}mv^2 = mgh \) represents this relationship, equating kinetic energy at launch to potential energy at maximum height. Knowing that the total energy remains the same simplifies calculations and predictions regarding the projectile's path. Mastering this principle allows for practical and theoretical predictions of a projectile's behavior.
Horizontal Range
The horizontal range is the total horizontal distance traveled by a projectile. This is one of the critical variables that helps in determining the effectiveness of a projectile's path. It essentially measures how far the projectile lands from the point of launch along the horizontal axis.
The formula used to calculate horizontal range in the solution is \( R = \frac{v_0^2 \sin(2\theta)}{g} \). This formula considers both the initial velocity and the launch angle, providing a comprehensive method to calculate the range. By setting \( \theta = 30^{\circ} \), they found the range \( R = 4h\sqrt{3} \). This section in problem-solving is crucial for students seeking to understand how launch variables affect projectile reach, helping in strategic planning and analysis of projectile mechanics.

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