Calculate Resistive Force of Water on Speedboat | 130 hp Required for 15 m/s

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In summary, a speedboat requires 130 hp to move at a constant speed of 15 m/s and the resistive force due to the water at that speed is 6.47x10^3 N.
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BrainMan
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Homework Statement


A speedboat requires 130 hp move at a constant speed of 15 m/s. Calculate the resistive force due to the water at that speed.


Homework Equations


P=F(V)


The Attempt at a Solution


I attempted to use Newtons first law that says in order for a object to be at rest the sum of the forces must be zero. Therefore I thought that the horsepower for the force of friction must be the same as the propulsion. So
130=F(15)
F= 8.6
The answer is 6.47x10^3 N or 1450 lbs
 
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  • #2
BrainMan said:

Homework Statement


A speedboat requires 130 hp move at a constant speed of 15 m/s. Calculate the resistive force due to the water at that speed.


Homework Equations


P=F(V)


The Attempt at a Solution


I attempted to use Newtons first law that says in order for a object to be at rest the sum of the forces must be zero. Therefore I thought that the horsepower for the force of friction must be the same as the propulsion. So
130=F(15)
F= 8.6
The answer is 6.47x10^3 N or 1450 lbs
The problem is with the units.

Horsepower is not an SI unit.
 
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F = 8.6 what? What are the units? You forgot to convert the units to some consistent system. hp is a British unit while m/s is International.
 
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BrainMan said:

Homework Statement


A speedboat requires 130 hp move at a constant speed of 15 m/s. Calculate the resistive force due to the water at that speed.


Homework Equations


P=F(V)


The Attempt at a Solution


I attempted to use Newtons first law that says in order for a object to be at rest the sum of the forces must be zero. Therefore I thought that the horsepower for the force of friction must be the same as the propulsion. So
130=F(15)
F= 8.6
The answer is 6.47x10^3 N or 1450 lbs

There's a standard conversion from hp to kW that every petrolhead will be familiar with. Use that conversion (google it) and work purely in SI units.
 
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OK I see what I did and found out how to solve the problem. Thanks everyone!
 

FAQ: Calculate Resistive Force of Water on Speedboat | 130 hp Required for 15 m/s

1. What is the formula for calculating the resistive force of water on a speedboat?

The formula for calculating the resistive force of water on a speedboat is F = 0.5 * p * v^2 * Cd * A, where F is the resistive force, p is the density of water, v is the speed of the boat, Cd is the drag coefficient, and A is the cross-sectional area of the boat.

2. How do I determine the required horsepower for a speedboat traveling at 15 m/s?

To determine the required horsepower for a speedboat traveling at 15 m/s, you can use the formula Power = Force * Velocity. In this case, the force is the resistive force of water and the velocity is 15 m/s. So, the required horsepower would be Power = F * 15.

3. What is the role of the drag coefficient in calculating the resistive force of water?

The drag coefficient represents the resistance of the boat's shape and design to the flow of water. A higher drag coefficient means the boat will experience more resistance and require more horsepower to maintain a certain speed.

4. How does the cross-sectional area of the boat affect the resistive force of water?

The cross-sectional area of the boat directly affects the resistive force of water. The larger the cross-sectional area, the more surface area of the boat is in contact with the water, resulting in a higher resistive force and requiring more horsepower to overcome it.

5. Can I use this formula to calculate the resistive force of water for any type of boat?

Yes, this formula can be used to calculate the resistive force of water for any type of boat. However, keep in mind that the values for density, drag coefficient, and cross-sectional area may vary depending on the specific design and characteristics of the boat.

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