The Speed of the Water Stream

Oct 13, 2025 by wbrum.org 28 views

Introduction

A fire hose shoots water horizontally 8 meters and only drops 20 centimeters. This seemingly simple scenario can be used to understand the physics behind the motion of objects under the influence of gravity. In this article, we will explore the speed of the water stream, the range of the hose at 25 degrees, and its maximum range.

The Speed of the Water Stream

To find the speed of the water stream, we need to consider the horizontal and vertical components of the motion. Since the water is shot horizontally, the initial vertical velocity is zero. However, due to the acceleration caused by gravity, the water will start to drop. We can use the equation of motion under gravity to find the speed of the water stream.

The equation of motion under gravity is given by:

y = y0 + v0t - (1/2)gt^2

where y is the final position, y0 is the initial position, v0 is the initial velocity, t is time, and g is the acceleration due to gravity.

In this case, the initial position is 8 meters (the horizontal distance), and the final position is 8 meters - 0.2 meters (the horizontal distance minus the drop). We can rearrange the equation to solve for time:

t = sqrt(2y / g)

Substituting the values, we get:

t = sqrt(2 * 8 / 9.8) ≈ 1.02 seconds

Now, we can use the equation of motion to find the speed of the water stream:

v = v0 + gt

Since the initial vertical velocity is zero, the speed of the water stream is:

v = gt ≈ 9.8 * 1.02 ≈ 10.0 m/s

The Range of the Hose at 25 Degrees

To find the range of the hose at 25 degrees, we need to consider the horizontal and vertical components of the motion. We can use the equation of motion under gravity to find the range.

The equation of motion under gravity is given by:

y = y0 + v0t - (1/2)gt^2

We can rearrange the equation to solve for time:

t = sqrt(2y / g)

Substituting the values, we get:

t = sqrt(2 * 8 / 9.8) ≈ 1.02 seconds

Now, we can use the equation of motion to find the range:

R = v0t cos(θ)

where R is the range, v0 is the initial velocity, t is time, and θ is the angle of projection.

Substituting the values, we get:

R = 10.0 * 1.02 * cos(25) ≈ 8.5 meters

The Maximum Range

To find the maximum range, we need to consider the angle of projection. The maximum range occurs when the angle of projection is 45 degrees.

The equation of motion under gravity is given by:

y = y0 + v0t - (1/2)gt^2

We can rearrange the equation to solve for time:

t = sqrt(2y / g)

Substituting the values, we get:

t = sqrt(2 * 8 / 9.8) ≈ 1.02 seconds

Now, we can use the equation of motion to find the maximum range:

R = v0t cos(45)

where R is the range, v0 is the initial velocity, t is time, and θ is the angle of projection.

Substituting the values, we get:

R = 10.0 * 1.02 * cos(45) ≈ 7.2 meters

Conclusion

In this article, we explored the physics behind a fire hose's water stream. We found the speed of the water stream to be approximately 10.0 m/s. We also found the range of the hose at 25 degrees to be approximately 8.5 meters and the maximum range to be approximately 7.2 meters.

References

[1] Halliday, D., Resnick, R., & Walker, J. (2013). Fundamentals of Physics. John Wiley & Sons.
[2] Serway, R. A., & Jewett, J. W. (2018). Physics for Scientists and Engineers. Cengage Learning.

Mathematical Derivations

Derivation of the Speed of the Water Stream

The equation of motion under gravity is given by:

y = y0 + v0t - (1/2)gt^2

We can rearrange the equation to solve for time:

t = sqrt(2y / g)

Substituting the values, we get:

t = sqrt(2 * 8 / 9.8) ≈ 1.02 seconds

Now, we can use the equation of motion to find the speed of the water stream:

v = v0 + gt

Since the initial vertical velocity is zero, the speed of the water stream is:

v = gt ≈ 9.8 * 1.02 ≈ 10.0 m/s

Derivation of the Range of the Hose at 25 Degrees

The equation of motion under gravity is given by:

y = y0 + v0t - (1/2)gt^2

We can rearrange the equation to solve for time:

t = sqrt(2y / g)

Substituting the values, we get:

t = sqrt(2 * 8 / 9.8) ≈ 1.02 seconds

Now, we can use the equation of motion to find the range:

R = v0t cos(θ)

where R is the range, v0 is the initial velocity, t is time, and θ is the angle of projection.

Substituting the values, we get:

R = 10.0 * 1.02 * cos(25) ≈ 8.5 meters

Derivation of the Maximum Range

The equation of motion under gravity is given by:

y = y0 + v0t - (1/2)gt^2

We can rearrange the equation to solve for time:

t = sqrt(2y / g)

Substituting the values, we get:

t = sqrt(2 * 8 / 9.8) ≈ 1.02 seconds

Now, we can use the equation of motion to find the maximum range:

R = v0t cos(45)

where R is the range, v0 is the initial velocity, t is time, and θ is the angle of projection.

Substituting the values, we get:

Q: What is the speed of the water stream?

A: The speed of the water stream is approximately 10.0 m/s. This is calculated using the equation of motion under gravity, taking into account the horizontal and vertical components of the motion.

Q: How does the angle of projection affect the range of the hose?

A: The angle of projection affects the range of the hose by changing the horizontal and vertical components of the motion. The maximum range occurs when the angle of projection is 45 degrees.

Q: What is the range of the hose at 25 degrees?

A: The range of the hose at 25 degrees is approximately 8.5 meters. This is calculated using the equation of motion under gravity, taking into account the horizontal and vertical components of the motion.

Q: What is the maximum range of the hose?

A: The maximum range of the hose is approximately 7.2 meters. This occurs when the angle of projection is 45 degrees.

Q: How does the height of the hose affect the range of the water stream?

A: The height of the hose does not affect the range of the water stream. The range of the water stream is determined by the horizontal and vertical components of the motion, which are independent of the height of the hose.

Q: Can the range of the hose be increased by increasing the angle of projection?

A: Yes, the range of the hose can be increased by increasing the angle of projection. However, there is an optimal angle of projection, which is 45 degrees, at which the maximum range is achieved.

Q: How does the speed of the water stream affect the range of the hose?

A: The speed of the water stream affects the range of the hose by changing the horizontal and vertical components of the motion. A faster water stream will result in a longer range.

Q: Can the range of the hose be increased by increasing the speed of the water stream?

A: Yes, the range of the hose can be increased by increasing the speed of the water stream. However, there is a limit to how fast the water stream can be increased before the range begins to decrease.

Q: What are some real-world applications of the physics behind a fire hose's water stream?

A: The physics behind a fire hose's water stream has many real-world applications, including:

Firefighting: Understanding the physics behind a fire hose's water stream is crucial for effective firefighting.
Water supply systems: The physics behind a fire hose's water stream is also important for designing and operating water supply systems.
Engineering: The physics behind a fire hose's water stream is used in the design and development of various engineering systems, including hydraulic systems and fluid dynamics.

Q: What are some common misconceptions about the physics behind a fire hose's water stream?

A: Some common misconceptions about the physics behind a fire hose's water stream include:

The range of the hose is determined by the height of the hose.
The speed of the water stream is the only factor that affects the range of the hose.
The angle of projection has no effect on the range of the hose.

Q: How can I learn more about the physics behind a fire hose's water stream?

A: There are many resources available for learning more about the physics behind a fire hose's water stream, including:

Textbooks: There are many textbooks available that cover the physics behind a fire hose's water stream.
Online resources: There are many online resources available, including videos, articles, and tutorials.
Courses: There are many courses available that cover the physics behind a fire hose's water stream, including online courses and in-person courses.

Conclusion

The physics behind a fire hose's water stream is a complex and fascinating topic that has many real-world applications. By understanding the physics behind a fire hose's water stream, we can design and operate more effective firefighting systems, water supply systems, and engineering systems.