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A ship is traveling due east at \(10 \mathrm{~km} / \mathrm{h}\). What must be the speed of a second ship heading \(30^{\circ}\) east of north if it is always due north of the first ship?

Short Answer

Expert verified
Ship B's speed must be 20 km/h.

Step by step solution

01

Understanding the Scenario

We have two ships, Ship A and Ship B. Ship A is moving due east at a speed of 10 km/h. Ship B is moving in a direction that is 30° east of north. Ship B needs to stay always directly north of Ship A.
02

Decompose Ship B's Velocity

Since Ship B is heading 30° east of north, its velocity can be separated into two components: a northward (vertical) component and an eastward (horizontal) component. We denote Ship B's speed as \( v \). The northward component is \( v \cdot \cos(30^{\circ}) \) and the eastward component is \( v \cdot \sin(30^{\circ}) \).
03

Setting Velocity Conditions

For Ship B to always remain due north of Ship A, the eastward (horizontal) components of their velocities must be equal. Therefore, the eastward velocity of Ship B must match the eastward velocity of Ship A, which is 10 km/h. This gives us the equation: \( v \cdot \sin(30^{\circ}) = 10 \).
04

Solving for Ship B's Speed

Using \( \sin(30^{\circ}) = 0.5 \), we substitute into the equation: \( v \cdot 0.5 = 10 \). Solving for \( v \), we get \( v = \frac{10}{0.5} = 20 \). Thus, Ship B must travel at 20 km/h to maintain being due north of Ship A.

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Key Concepts

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

Vector Decomposition
In physics, vector decomposition is a technique used to break a vector into its component parts. Think of a vector as an arrow that has both a direction and a magnitude. When you want to understand how this vector behaves in a certain scenario, it helps to break it down into its vertical and horizontal components. This makes it easier to analyze and solve problems.

For instance, in the example provided, Ship B's velocity is a vector because it has both a speed and a direction. To analyze this, we decompose it into two separate components:
  • The northward component, which shows how much of Ship B's velocity is directed towards the north.
  • The eastward component, which indicates how much of Ship B's velocity is directed toward the east.
By expressing these components mathematically, you can use trigonometry to solve problems regarding directions, such as keeping Ship B always due north of Ship A.
Trigonometry in Physics
Trigonometry is a branch of mathematics that studies the relationships between the angles and sides of triangles. In physics, it is especially useful to solve problems involving vectors and directional components.

In the context of the provided exercise, we applied trigonometry to determine the components of Ship B's velocity. Ship B is moving 30° east of north, which forms a right triangle when observed as vector decomposition.

The northward component of the velocity can be calculated using the cosine function: \[ v_n = v \cdot \cos(30^{\circ}) \]

And, the eastward component using the sine function:\[ v_e = v \cdot \sin(30^{\circ}) \]

Here:
  • \(\cos(30^{\circ})\) gives us the portion of Ship B's velocity directed northward.
  • \(\sin(30^{\circ})\) provides the part of Ship B's velocity directed eastward.
Use these calculations to set conditions for relative motion, keeping one object in a particular position relative to another.
Directional Components of Velocity
To maintain the relative position of objects moving in space, understanding their directional components of velocity is crucial. Each component of velocity represents how fast an object is moving in a particular direction.

In the exercise, Ship A moves strictly east at 10 km/h. Meanwhile, Ship B, moving at an unspecified speed initially, needs its components adjusted to maintain it due north of Ship A. Specifically, the condition is:
  • The eastward component of Ship B's velocity should equal Ship A's velocity.
Given the calculation process reveals:\[ v \cdot \sin(30^{\circ}) = 10 \]

Where:
  • \(\sin(30^{\circ})\) is known to be 0.5, allowing us to conclude that Ship B must travel at 20 km/h to satisfy this condition.
This ensures that the eastward motion of Ship B equals that of Ship A, thus keeping Ship B directly north of Ship A, with its northward component allowing it to maintain this position dynamics.

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Most popular questions from this chapter

A runner travels \(1.5\) laps around a circular track in a time of \(50 \mathrm{~s}\). The diameter of the track is \(40 \mathrm{~m}\) and its circumference is \(126 \mathrm{~m}\). Find \((a)\) the average speed of the runner and \((b)\) the magnitude of the runner's average velocity. Be careful here; average speed depends on the total distance traveled, whereas average velocity depends on the displacement at the end of the particular journey.

A 12-mg housefly has a maximum speed of \(4.5\) mph; what is that in \(\mathrm{m} / \mathrm{s}\) ? [ Hint: 2 significant figures. \(1 \mathrm{mph}=0.44707 \mathrm{~m} / \mathrm{s}\).] \(\mathbf{1 . 2 1}\) [I] According to its computer, a robot that left its closet and traveled \(1200 \mathrm{~m}\), had an average speed of \(20.0 \mathrm{~m} / \mathrm{s}\). How long did the trip take?

A boat can travel at a speed of \(8 \mathrm{~km} / \mathrm{h}\) in still water on a lake. In the flowing water of a stream, it can move at \(8 \mathrm{~km} / \mathrm{h}\) relative to the water in the stream. If the stream speed is \(3 \mathrm{~km} / \mathrm{h}\), how fast can the boat move past a tree on the shore when it is traveling \((a)\) upstream and \((b)\) downstream? (a) If the water was standing still, the boat's speed past the tree would be \(8 \mathrm{~km} / \mathrm{h}\). But the stream is carrying it in the opposite direction at \(3 \mathrm{~km} / \mathrm{h}\). Therefore, the boat's speed relative to the tree is \(8 \mathrm{~km} / \mathrm{h}-3 \mathrm{~km} / \mathrm{h}=5 \mathrm{~km} / \mathrm{h}\). (b) In this case, the stream is carrying the boat in the same direction the boat is trying to move. Hence, its speed past the tree is \(8 \mathrm{~km} / \mathrm{h}+3 \mathrm{~km} / \mathrm{h}=11 \mathrm{~km} / \mathrm{h}\).

What displacement must be added to a 50 -cm displacement in the \(+x\) -direction to give a resultant displacement of \(85 \mathrm{~cm}\) at \(25^{\circ}\) ?

A student driving a car travels \(10.0 \mathrm{~km}\) in \(30.0\) min. What was her average speed? The defining equation is \(u_{a v}=l / t\). Here \(l\) is in kilometers, and \(t\) is in minutes, so the first thing to do is convert \(10.0 \mathrm{~km}\) to meters and then \(30.0\) min into seconds: \((10.0 \mathrm{~km})(1000 \mathrm{~m} / \mathrm{km})=10.0 \times\) \(10^{3} \mathrm{~m}\) and \((30.0 \mathrm{~min}) \times(60.0 \mathrm{~s} / \mathrm{min})=1800 \mathrm{~s}\). We need to solve for \(v_{a u}\), giving the numerical answer to three significant figures: $$ v_{a v}=\frac{l}{t}=\frac{10.0 \times 10^{3} \mathrm{~m}}{1800 \mathrm{~s}}=5.56 \mathrm{~m} / \mathrm{s} $$

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