/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 75 A train travels due south at \(3... [FREE SOLUTION] | 91Ó°ÊÓ

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A train travels due south at \(30 \mathrm{~m} / \mathrm{s}\) (relative to the ground) in a rain that is blown toward the south by the wind. The path of each raindrop makes an angle of \(70^{\circ}\) with the vertical, as measured by an observer stationary on the ground. An observer on the train, however, sees the drops fall perfectly vertically. Determine the speed of the raindrops relative to the ground.

Short Answer

Expert verified
The raindrops' speed relative to the ground is approximately 31.9 m/s.

Step by step solution

01

Understanding the Problem

We are given a train moving south at 30 m/s and raindrops that make a 70° angle with the vertical when observed from the ground. From the train, the raindrops appear to fall vertically. We need to find the speed of the raindrops relative to the ground.
02

Identify the Known Values and Relate Velocities

The train's speed relative to the ground is 30 m/s going south. The raindrops make a 70° angle with the vertical from the ground observer's perspective. The train observer sees raindrops falling vertically. The horizontal component of the raindrop's velocity as seen from the train equals the train's speed, 30 m/s.
03

Use Trigonometry to Relate Speed and Angle

Let the speed of the raindrops relative to the ground be \(v_r\). The horizontal component of this speed (towards south) is \(v_r \sin(70^")\). This horizontal component balances with the train's speed, yielding \(v_r \sin(70^") = 30\).
04

Calculate the Speed of the Raindrops

Solve for \(v_r\) using \(v_r = \frac{30}{\sin(70^\circ)}\).
05

Perform the Calculation

Calculate using the sine of 70 degrees: \(v_r \approx \frac{30}{0.9397} \approx 31.9\) m/s.

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Key Concepts

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

Trigonometry in Physics
Trigonometry plays a crucial role in physics, especially when dealing with problems involving angles and motion. In this exercise, trigonometric functions help us understand how different velocities relate to each other.
By using trigonometry, we're able to break down the velocity of the rain into components. These components help us understand the rain's actual path when influenced by both velocity and wind.
  • The vertical component of velocity is handled separately from the horizontal component.
  • The horizontal component is what helps us balance the rain's angle and the train's motion.
Using sine, cosine, and tangent, we can figure out how objects move relative to different observers. For instance, when calculating the speed of the raindrop relative to the ground, the expression involves sine. The function relates the angle to its true velocity.
This approach is a common tool in physics, aiding in decoding complicated motion scenarios.
Angle of Motion
The angle of motion is critical in this exercise. Here, the raindrops create an angle of 70° with the vertical from the ground observer's point of view.
Understanding these angles is necessary to grasp how motion appears from different perspectives.
The angle provides valuable information about how the raindrop's velocity components behave:
  • The angle between the motion and a reference line (like the vertical in this case) reveals how much the motion is tilted.
  • By determining this angle, we can find out how the velocities divide into horizontal and vertical components using trigonometry.
For the train observer, the motion appears different since the horizontal component aligns with the train's direction.
The angle also clarifies how the observer's motion influences perceived angles and speeds.
Rain and Wind Motion
In this problem, rain and wind motion are crucial for understanding relative velocity. When rain falls, it does not always hit the ground vertically due to wind effects.
The motion of rain gives a real-world illustration of relative motion experienced in daily life.
Here's how it works:
  • The wind blows against the rain, causing it to move at an angle. From an observer on the ground, this angle is different than what someone in a moving vehicle would see.
  • When you are on the train, the raindrops appear to fall vertically because your relative motion changes how you perceive the rain's path.
Essentially, how we see movement is relative to our motion. The exercise also highlights the interaction between wind and rain, showcasing how ever-present forces in our environment influence how natural phenomena are observed and understood.
By recognizing these dynamics, students can visualize and calculate different motions as they would appear to moving observers.

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Most popular questions from this chapter

An Earth satellite moves in a circular orbit \(640 \mathrm{~km}\) (uniform circular motion) above Earth's surface with a period of \(98.0 \mathrm{~min} .\) What are (a) the speed and (b) the magnitude of the centripetal acceleration of the satellite?

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You are to throw a ball with a speed of \(12.0 \mathrm{~m} / \mathrm{s}\) at a target that is height \(h=5.00 \mathrm{~m}\) above the level at which you release the ball (Fig. \(4-58\) ). You want the ball's velocity to be horizontal at the instant it reaches the target. (a) At what angle \(\theta\) above the horizontal must you throw the ball? (b) What is the horizontal distance from the release point to the target? (c) What is the speed of the ball just as it reaches the target?

A woman can row a boat at \(6.40 \mathrm{~km} / \mathrm{h}\) in still water. (a) If she is crossing a river where the current is \(3.20 \mathrm{~km} / \mathrm{h},\) in what direction must her boat be headed if she wants to reach a point directly opposite her starting point? (b) If the river is \(6.40 \mathrm{~km}\) wide, how long will she take to cross the river? (c) Suppose that instead of crossing the river she rows \(3.20 \mathrm{~km}\) down the river and then back to her starting point. How long will she take? (d) How long will she take to row \(3.20 \mathrm{~km}\) up the river and then back to her starting point? (e) In what direction should she head the boat if she wants to cross in the shortest possible time, and what is that time?

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