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In a fireworks display, a rocket is launched from the ground with a speed of 18.0 m/s and a direction of 51.0\(^\circ\) above the horizontal. During the flight, the rocket explodes into two pieces of equal mass (see Fig. 8.32). (a) What horizontal distance from the launch point will the center of mass of the two pieces be after both have landed on the ground? (b) If one piece lands a horizontal distance of 26.0 m from the launch point, where does the other piece land?

Short Answer

Expert verified
(a) 32.3 m; (b) 38.6 m.

Step by step solution

01

Analyze Initial Conditions

The rocket is launched with an initial velocity of 18.0 m/s at an angle of 51.0° above the horizontal. We need the horizontal component of this velocity, which is \( v_{0x} = v_0 \cos(\theta) \). Calculating this: \( v_{0x} = 18.0 \cos(51.0^\circ) \approx 11.3 \text{ m/s} \).
02

Calculate Total Time of Flight

The vertical component of the initial velocity \( v_{0y} = v_0 \sin(\theta) \approx 18.0 \sin(51.0^\circ) = 14.0 \text{ m/s} \). Time to reach maximum height is \( t_{up} = \frac{v_{0y}}{g} \approx \frac{14.0}{9.8} \approx 1.43 \text{ s} \). Total time of flight is \( 2t_{up} = 2 \times 1.43 \approx 2.86 \text{ s} \).
03

Calculate Horizontal Distance of Center of Mass

The horizontal distance traveled by the center of mass is \( x = v_{0x} \times \text{Total time} = 11.3 \times 2.86 \approx 32.3 \text{ m} \). Therefore, the center of mass travels 32.3 meters.
04

Determine Distance of Second Piece

The first piece lands 26.0 m from the launch point. Let the distance of the second piece be \( d \). Since they have equal mass, the center of mass distance is the average of their distances: \( \frac{26.0 + d}{2} = 32.3 \). Solving for \( d \), we find \( d = 2 \times 32.3 - 26.0 = 38.6 \text{ m} \).

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Key Concepts

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

Center of Mass
The center of mass is an essential concept in physics, representing a point where the total mass of a system can be considered to concentrate. In projectile motion, the center of mass helps us understand how a system behaves when external forces, such as gravity, act on it. For a projectile that bursts into multiple pieces, the center of mass continues on the original trajectory it would have had if the explosion had not occurred. This is due to the conservation of momentum, which states that the overall motion of the center of mass is unaffected by internal forces such as explosions. For the exercise in question, this principle allows us to compute the horizontal distance the center of mass will travel, using initial conditions before any explosion occurs.
Horizontal Distance
In projectile motion, horizontal distance is a crucial parameter that describes how far a projectile travels horizontally before it lands. This is influenced by factors such as initial speed, launch angle, and gravity but is not affected by vertical motions. To calculate it, you can use the horizontal component of the initial velocity along with the total time of flight. The formula to find the horizontal distance, assuming no air resistance, is:
  • Horizontal Distance = Horizontal Velocity × Time of Flight
This distance helps in predicting where each piece will land if the projectile happens to break apart. In our exercise, knowing the launch angle and initial speed allowed us to compute the horizontal velocity and therefore accurately predict the horizontal motion of the rocket.
Time of Flight
The time of flight is the duration a projectile remains in the air from the point of launch until it touches the ground. It depends on the vertical component of the initial velocity and gravity. For our rocket, calculating the time of flight involves determining how long it takes to reach maximum height and then doubling it, since the time to ascend and descend are equal when neglecting air resistance.
  • Time to reach maximum height: \[ t_{up} = \frac{v_{0y}}{g} \]
  • Total time of flight: \[ 2t_{up} \]
This time determines how long the horizontal components of velocity influence the trajectory, thus impacting the horizontal distance covered by each piece of the exploded rocket.
Explosion Impact on Trajectory
An explosion occurring in airborne projectiles can appreciably affect their trajectory. However, the explosion itself does not disturb the trajectory of the center of mass of the object. This is due to the conservation of linear momentum, which dictates that internal forces, such as those from an explosion, do not affect external motion. Therefore, in our scenario, even with the rocket splitting into two pieces, the center of mass follows the same path it would have taken if it had not exploded. This unobstructed trajectory enables us to predict where the center of mass will land on the ground, which in turn helps determine the landing positions of individual pieces when combined with other known distances.

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