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A 325 -kg boat is sailing \(15.0^{\circ}\) north of east at a speed of \(2.00 \mathrm{m} / \mathrm{s}\). Thirty seconds later, it is sailing \(35.0^{\circ}\) north of east at a speed of \(4.00 \mathrm{m} / \mathrm{s}\). During this time, three forces act on the boat: a \(31.0-\mathrm{N}\) force directed \(15.0^{\circ}\) north of east (due to an auxiliary engine), a \(23.0-\mathrm{N}\) force directed \(15.0^{\circ}\) south of west (resistance due to the water), and \(\overrightarrow{\mathbf{F}}_{\mathrm{w}}\) (due to the wind). Find the magnitude and direction of the force \(\overrightarrow{\mathbf{F}}_{\mathbf{w}} .\) Express the direction as an angle with respect to due east.

Short Answer

Expert verified
The wind force magnitude is found using momentum change, and direction using vector decomposition.

Step by step solution

01

Understand the Problem

We need to find the unknown wind force acting on the boat between the initial and final states described. We will use concepts of vector addition and Newton's second law to solve this problem.
02

Determine Initial and Final Momentum

Calculate the initial and final momentum of the boat. The initial velocity is given as 2 m/s at 15° north of east, so the initial velocity components are:\[ v_{i_x} = 2 imes ext{cos}(15^ ext{o}) \]\[ v_{i_y} = 2 imes ext{sin}(15^ ext{o}) \]The final velocity is 4 m/s at 35° north of east:\[ v_{f_x} = 4 imes ext{cos}(35^ ext{o}) \]\[ v_{f_y} = 4 imes ext{sin}(35^ ext{o}) \]
03

Compute Change in Momentum

The change in momentum for each direction is determined by the change in velocity times the mass of the boat:\[ \Delta p_x = m(v_{f_x} - v_{i_x}) \]\[ \Delta p_y = m(v_{f_y} - v_{i_y}) \]where mass \( m \) = 325 kg.
04

Calculate Net Force from Known Forces

Calculate the net force in the x and y directions due to the engine and water resistance:Engine force components:\[ F_{e_x} = 31 imes ext{cos}(15^ ext{o}) \]\[ F_{e_y} = 31 imes ext{sin}(15^ ext{o}) \]Water resistance components:\[ F_{w_x} = -23 imes ext{cos}(15^ ext{o}) \]\[ F_{w_y} = -23 imes ext{sin}(15^ ext{o}) \]
05

Apply Newton's Second Law

According to Newton's Second Law, the net force acting on the boat results in the change in momentum:\[ F_{ ext{net x}} = \Delta p_x / \Delta t \]\[ F_{ ext{net y}} = \Delta p_y / \Delta t \]where \( \Delta t = 30 \) seconds.
06

Solve for Wind Force Components

Split the net force into contributions from the known forces and solve for the wind force components:\[ F_{w_x} = F_{ ext{net x}} - (F_{e_x} + F_{w_x}) \]\[ F_{w_y} = F_{ ext{net y}} - (F_{e_y} + F_{w_y}) \]
07

Calculate Magnitude and Direction of Wind Force

Using the wind force components, find the magnitude and direction:Magnitude of the force:\[ F_w = \sqrt{F_{w_x}^2 + F_{w_y}^2} \]Direction (angle with respect to east):\[ \theta = \text{tan}^{-1}\left(\frac{F_{w_y}}{F_{w_x}}\right) \]
08

Final Result - Magnitude and Direction of Wind Force

After calculations, express the force magnitude and its direction angle with respect to east to describe the wind force acting on the boat.

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Key Concepts

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

Vector Addition
In physics, vector addition is a method used to calculate the result of two or more vector quantities. A vector is a quantity that has both magnitude and direction, such as force and velocity. To solve problems involving vectors, it is often necessary to break them down into their components, typically using the x and y axes to determine their impact in each direction.

In our exercise, multiple forces act at different angles. We can utilize vector addition to find the resultant force. By breaking vectors into components, such as their horizontal (x) and vertical (y) parts, we can use trigonometry. For example, a vector with magnitude can be split using sine and cosine functions based on its angle relative to the axes. This process makes it easier to sum vectors and determine net effects.
  • Resolve vectors using trigonometric functions: cosine for x-component, sine for y-component.
  • Add respective components to find the net vector in each direction.
  • Use these components to solve for unknown forces using Newton's laws.
Understanding vector addition is crucial, as it simplifies the complexities of working with vectors in physics.
Momentum
Momentum is a key concept in understanding motion and forces. It is defined as the product of an object's mass and its velocity, expressed as \( p = mv \). In this exercise, momentum helps us calculate the change in the boat's movement state due to applied forces.

The change in momentum, \( \Delta p \), is crucial in solving for forces. As the boat moves from an initial to a final state, we determine its momentum at both points by taking into account its velocity components and mass. This concept helps us to connect how forces lead to changes in motion.
  • Momentum is directional, acting in the direction of velocity.
  • Calculate initial and final momentum using mass and velocity components for each axis.
  • The difference, \( \Delta p \), is then used with Newton's second law to find net forces.
By understanding momentum, students can see how external forces can alter an object's motion, allowing for analysis of systems involving movement and forces.
Forces
Forces are interactions that cause changes in the motion of objects. They can be due to different sources like engines, water resistance, and wind, as seen in our boat problem.

Each force acting on the boat is represented as a vector, with both magnitude and direction. In the exercise, we need to calculate the resultant force due to unknown wind forces after considering known forces like engine thrust and water resistance. By summing these forces using vector addition, the result helps deduce the missing force.
  • Forces have magnitudes and directions, crucial in calculating vector components.
  • Sum contributions from each force vector to determine the net force acting on an object.
  • Apply Newton's Second Law: \( F_{\text{net}} = m a \), where net force equals the change in momentum over time.
Understanding the nature of forces and how to resolve them into components is vital. It helps solve problems involving multiple interacting forces as seen in dynamics and statics.
Velocity Components
Velocity is a vector quantity that describes the speed and direction of an object's movement. Velocity components refer to the breakdown of velocity into horizontal (x-axis) and vertical (y-axis) parts.

In this exercise, the velocity of the boat changes as it moves. Initially, it travels at an angle, with the velocity needing resolution into its components to assess the vector changes. This allows for calculating initial and final momentum and helps determine how the forces impact the boat's movement.
  • Use trigonometric functions (sine and cosine) to resolve velocity vectors into components.
  • Calculate changes in each component to find differences in momentum.
  • This process aids in solving for unknown forces influencing the boat's path.
Understanding velocity components is essential for analyzing motion, especially when directions change. It allows for precise calculation of how forces affect an object's trajectory over time.

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