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A \(3.00-\mathrm{g}\) leaf is dropped from a height of \(2.00 \mathrm{m}\) above the ground. Assume the net downward force exerted on the leaf is \(F=m g-b v,\) where the drag factor is \(b=0.0300 \mathrm{kg} / \mathrm{s} .\) (a) Calculate the terminal speed of the leaf. (b) Use Euler's method of numerical analysis to find the speed and position of the leaf, as functions of time, from the instant it is released until \(99 \%\) of terminal speed is reached. (Suggestion: Try \(\Delta t=0.005 \mathrm{s} .\) )

Short Answer

Expert verified
The terminal speed of the leaf is 980 cm/s. The speed and position as a function of time can be found using Euler's method, stopping when the speed reaches 970.2 cm/s, which is 99% of the terminal speed. The exact speed and position at each time interval could be expressed as numerical data or a graph, depending on the output of the program used.

Step by step solution

01

Calculate Terminal Speed

Set up the equation for terminal speed where the net force exerted on the leaf is 0. Therefore: \(0=m g-b v\). Solve this for \(v\), yielding a terminal speed equation of \(v = mg / b\). Now simply plug the given values: \(v = (3.00g \times 9.8m/s^2) / 0.0300 kg/s = 980 cm/s\).
02

Initialize Variables for Euler's Method

Set the initial conditions. Let \(t = 0\), \(v = 0\), \(y = 2.0m\) (the starting height), and \(\Delta t = 0.005s\). We also already know \(g = 9.8 m/s^2\), \(m = 3.00g = 0.003kg\), and \(b = 0.0300 kg/s\). Set a variable \(v_t\) as the target speed (99% of terminal speed), which is \(0.99 \times 980 cm/s = 970.2 cm/s\).
03

Apply Euler's Method

Now implement Euler's method iteratively to find the speed and position as functions of time until the target speed is reached. Use the formulas \(\Delta v = ((mg - bv) / m )\Delta t\) and \(\Delta y = v \Delta t\). Update \(v\) and \(y\) by adding the \(\Delta v\) and \(\Delta y\) to each, and increment \(t\) by \(\Delta t\). Repeat these steps until \(v\) is close to or greater than \(v_t\). Euler's method models the continuous change in velocity and position over our small time steps. This step involves programming and is best done using a software such as Python or Matlab.

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Key Concepts

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

Terminal Speed Calculation
Understanding terminal speed is crucial when studying the dynamics of objects moving through fluids, like air. It represents the constant speed that an object eventually reaches when the force of gravity is balanced by the drag force. To calculate this, we set the net force acting on the object to zero and solve for velocity \(v\). If we have an equation of net force, \( F = mg - bv \), where \(m\) is the mass, \(g\) is the acceleration due to gravity, and \(b\) is the drag factor, the terminal speed \(v_t\) can be found by rearranging the equation to \(v_t = mg / b\).

In the given exercise, a leaf has the drag factor \(b=0.0300 \mathrm{kg/s}\) and a mass of \(3.00g\), which is \(0.003kg\). Using the acceleration due to gravity \(g = 9.8m/s^2\), we find that the terminal speed \(v_t = (0.003kg \times 9.8m/s^2) / 0.0300 kg/s \), which simplifies to \(v_t = 980 cm/s\). Terminal speed is relevant not only in physics problems but also in real-world applications like parachuting and the design of vehicles.
Numerical Analysis in Physics
Numerical analysis is the part of mathematics and computer science that creates, analyzes, and implements algorithms for solving mathematically defined problems numerically. In physics, it often involves the approximation of complex physical systems that are difficult to solve analytically. Euler's method is one such numerical technique used to approximate the solutions to ordinary differential equations which represent many physical phenomena, such as the motion of an object through a resisting medium.

The method is iterative, meaning it progresses step by step, and it starts by initializing variables at an initial condition. It then proceeds to update the variables over small increments of time, \( \Delta t \), using the known derivatives of these variables. In the context of the exercise, we need to know the speed \(v\) and position \(y\) of the leaf over time, and we apply Euler's method to find these values iteratively until we reach 99% of the terminal velocity. The small \( \Delta t \) chosen improves the accuracy of the results, yet it requires more computational steps.
Force and Motion
Force and motion are foundational concepts in physics that describe how objects interact and move. Newton's second law states that the force exerted on an object is equal to the mass of the object multiplied by its acceleration \( (F = ma) \). In our exercise, the motion of a falling leaf can be described by two forces: the gravitational force pulling it downward (weight \( mg \) and the drag force that opposes its motion through air (\( bv \)).

As the leaf falls, it accelerates until it reaches a point where the drag force is equal to the weight, resulting in zero net force and no further acceleration—this is when the leaf has reached terminal speed. The detailed steps involve calculating this terminal speed \(v_t\) and then using Euler's method to simulate the leaf's fall, updating its speed and position with time increments until the speed is approximately 99% of \(v_t\). By understanding the forces at play, physicists and engineers can predict the motion of objects under various conditions, which is essential in fields ranging from aeronautical engineering to meteorology.

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Most popular questions from this chapter

A 0.142-kg baseball has a terminal speed of \(42.5 \mathrm{m} / \mathrm{s}\) \((95 \mathrm{mi} / \mathrm{h}) \cdot\) (a) If a baseball experiences a drag force of magnitude \(R=C v^{2},\) what is the value of the constant \(C ?\) (b) What is the magnitude of the drag force when the speed of the baseball is \(36.0 \mathrm{m} / \mathrm{s} ?\) (c) Use a computer to determine the motion of a bascball thrown vertically upward at an initial speed of \(36 \mathrm{m} / \mathrm{s} .\) What maximum height does the ball reach? How long is it in the air? What is its speed just before it hits the ground?

Consider an object on which the net force is a resistive force proportional to the square of its speed. For example, assume that the resistive force acting on a speed skater is \(f=-k m v^{2},\) where \(k\) is a constant and \(m\) is the skater's mass. The skater crosses the finish line of a straight-line race with speed \(u_{0}\) and then slows down by coasting on his skates. Show that the skater's speed at any time \(t\) after crossing the finish line is \(v(t)=u_{0} /\left(1+k t u_{0}\right) .\) This problem also provides the background for the two following problems.

A space station, in the form of a wheel 120 m in diameter, rotates to provide an "artificial gravity" of \(3.00 \mathrm{m} / \mathrm{s}^{2}\) for persons who walk around on the inner wall of the outer rim. Find the rate of rotation of the wheel (in revolutions per minute) that will produce this effect.

If the coefficient of static friction between your coffee cup and the horizontal dashboard of your car is \(\mu_{s}=0.800\) how fast can you drive on a horizontal roadway around a right turn of radius \(30.0 \mathrm{m}\) before the cup starts to slide? If you go too fast, in what direction will the cup slide relative to the dashboard?

A person stands on a scale in an elevator. As the elevator starts, the scale has a constant reading of \(591 \mathrm{N}\). As the elevator later stops, the scale reading is \(391 \mathrm{N}\). Assume the magnitude of the acceleration is the same during starting and stopping, and determine (a) the weight of the person, (b) the person's mass, and (c) the acceleration of the elevator.

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