# What is the average force exerted by the water on the wall when it rebounds?

• longball4153
In summary: I think you are misunderstanding the average force equation. The average force is the average of the forces over the time interval.
longball4153

## Homework Statement

A horizontal stream of water from a fire-fighter's hose hits a vertical wall. The firefighter knows that 16.9 kg of water are emitted from the hose per second, and that the water has a speed of 45.5 m/s. At the instant when it hits the wall, the direction of the velocity vector of the water is 25.0 degrees BELOW the horizontal. Calculate the average force exerted by the water on the wall, assuming that the vertical component of the velocity vector of the water is unchanged but the horizontal component of the velocity vector is reversed when the water rebounds from the wall.

Vi=45.5 m/s
m= 16.9 kg/s
ϴ= 25 Degrees BELOW the horizontal

P=mv
v2=vo2+2ax

## The Attempt at a Solution

Po=mvo
po=16.9kg/s*45.5m/s
Po=768.95

Now I have the initial momentum. From here I am stuck and not sure where to go next. I know I need to somehow incorporate the angle given and calculate a final velocity. But then how would I take that and find an average force? Hopefully someone can explain/ show me the set up from here. Thanks!

An average force is defined as the sum of the forces applied divided by the period of time. For example, if you have force a for 1 second and force b for 2 seconds, then the average force is:

$$\frac{1s*F_a + 2s*F_b}{3s}$$ where s is seconds.

Does that help?

I understand that, however, how do I relate that to this particular problem?

I am doing this exact problem right now. I have found the momentum of the water and the x component of the velocity. Average force is the change in momentum/change in time, but how can you find time using the information in the problem?

## 1. What is the "Fire Hose Momentum Problem"?

The "Fire Hose Momentum Problem" is a physics problem that involves calculating the force exerted by a high-pressure fire hose on a person or object when the hose is turned on. This problem is often used to demonstrate the concept of momentum, which is the product of an object's mass and velocity.

## 2. How do you solve the Fire Hose Momentum Problem?

To solve the Fire Hose Momentum Problem, you need to know the mass and velocity of the water coming out of the fire hose, as well as the mass and velocity of the person or object being hit by the water. You can then use the formula for momentum (p=mv) to calculate the force exerted by the water on the person or object.

## 3. What factors affect the force exerted by a fire hose?

The force exerted by a fire hose is affected by several factors, including the mass and velocity of the water, the distance between the fire hose and the person or object, and the angle at which the water hits the person or object. Additionally, the shape and size of the nozzle on the fire hose can also impact the force exerted.

## 4. What are the real-world applications of the Fire Hose Momentum Problem?

The Fire Hose Momentum Problem has several real-world applications, including in the design and testing of fire hoses and other high-pressure water systems. It can also be used to understand the impact of water on structures during floods or other natural disasters.

## 5. How can understanding the Fire Hose Momentum Problem be helpful for firefighters?

By understanding the Fire Hose Momentum Problem, firefighters can better control the force and direction of water coming out of a fire hose. This can be especially important in situations where there are people or objects nearby, as the force of the water can cause injury or damage if not properly aimed and controlled.

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