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A rocket is fired at a speed of 75.0 m/s from ground level, at an angle of 60.0 above the horizontal. The rocket is fired toward an 11.0-m-high wall, which is located 27.0 m away. The rocket attains its launch speed in a negligibly short period of time, after which its engines shut down and the rocket coasts. By how much does the rocket clear the top of the wall?

Short Answer

Expert verified
The rocket clears the wall by approximately 6.5 meters.

Step by step solution

01

Identify initial components of velocity

First, we need to find the horizontal and vertical components of the initial velocity. The initial speed is given as 75.0 m/s and the launch angle is 60.0 degrees.- The horizontal component can be calculated using: \( v_{x0} = v_0 \cos(\theta) = 75.0 \cos(60^{\circ}) \)- The vertical component can be calculated using: \( v_{y0} = v_0 \sin(\theta) = 75.0 \sin(60^{\circ}) \) Where \( v_0 \) is the initial speed and \( \theta \) is the angle of launch.
02

Calculate the time to reach the wall horizontally

Using the horizontal velocity component, calculate the time it takes for the rocket to reach the wall which is 27.0 meters away.- Use the formula for horizontal motion: \( x = v_{x0} \cdot t \)Rearranging for time \( t \): \( t = \frac{x}{v_{x0}} = \frac{27.0}{v_{x0}} \)
03

Calculate the rocket's vertical height at the wall

Using the time calculated, determine the vertical position of the rocket when it is horizontally at the wall. We'll use the kinematic equation:\( y = v_{y0} \cdot t - \frac{1}{2} g t^2 \)Where:- \( y \) is the vertical position,- \( g = 9.81 \text{ m/s}^2 \) (acceleration due to gravity),- \( t \) is the time taken to reach the wall as calculated in the previous step.
04

Determine clearance over the wall

The last step is to compute the difference between the height of the rocket at the wall and the height of the wall itself. The vertical height at the wall can be found from Step 3.- Clearance height: \( \text{Clearance} = y - 11.0 \)where 11.0 m is the height of the wall.

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Key Concepts

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

Initial Velocity Components
When analyzing projectile motion, it's crucial to break down the initial velocity into its horizontal and vertical components. This helps us understand how the object will move in each direction. The initial speed of the rocket is 75.0 m/s and it's launched at a 60.0 degree angle from the horizontal. The horizontal component, denoted as \( v_{x0} \), can be found using the cosine of the launch angle: \( v_{x0} = 75.0 \cos(60^{\circ}) \). Similarly, the vertical component, \( v_{y0} \), is calculated using the sine of the angle: \( v_{y0} = 75.0 \sin(60^{\circ}) \). Calculating these components gives us a clear picture of how the rocket's initial velocity is divided between its horizontal and vertical motion.
Horizontal and Vertical Motion
In projectile motion, horizontal and vertical motions are treated independently.
  • **Horizontal Motion**: This motion is straightforward as there is no acceleration acting horizontally (if we neglect air resistance). The rocket will coast horizontally at a constant velocity determined by \( v_{x0} \). To calculate how long it takes to reach the wall horizontally, we use the formula \( x = v_{x0} \cdot t \). Solving for \( t \), we rearrange it as \( t = \frac{x}{v_{x0}} \).
  • **Vertical Motion**: Here, the rocket initially moves upward due to its vertical velocity component, \( v_{y0} \). However, gravity, acting at \( 9.81 \text{ m/s}^2 \), will counteract this upward motion, eventually bringing the rocket back down. The vertical position at any time \( t \) is given by the equation \( y = v_{y0} \cdot t - \frac{1}{2} g t^2 \).
These calculations provide insight into how the rocket moves both horizontally and vertically over time.
Kinematic Equations
Kinematic equations are powerful tools in describing the motion of objects, especially in projectile motion. They allow us to predict an object's position at any time given its initial velocity and acceleration. For the rocket, the following equations are most relevant:
  • **Horizontal Motion**: As previously stated, the horizontal distance traveled \( x \) is found using the equation \( x = v_{x0} \cdot t \). This embodies uniform linear motion since there is no horizontal acceleration.
  • **Vertical Motion**: The vertical motion is slightly more complex due to the influence of gravity. Here we use \( y = v_{y0} \cdot t - \frac{1}{2} g t^2 \) to find the rocket's height at any time \( t \). This equation accounts for the initial vertical velocity and the gravitational pull acting on the rocket.
Understanding these equations enables us to calculate the trajectory path of the projectile and predict where and when it will pass certain points, like the wall in this scenario.
Launch Angle Effects
The launch angle significantly impacts projectile motion, affecting both the horizontal range and maximum height. A launch angle of 0 degrees results in horizontal motion only, maximizing range but eliminating height. Meanwhile, a 90-degree angle maximizes height but provides no horizontal range. A 45-degree angle typically offers a balanced maximum range and height. However, in this exercise, the launch angle is 60 degrees, which means:
  • **Height**: The rocket will achieve a greater height compared to the range due to the increased vertical component.
  • **Range**: While the range isn't maximized, the steeper angle allows for a higher trajectory, which might be necessary to clear an obstacle, such as the 11-meter-high wall in this case.
Understanding how the launch angle influences the path of the projectile helps in making decisions about the trajectory needed to clear obstacles effectively.

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