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Two coconuts fall freely from rest at the same time, one from a tree twice as high as the other. (a) If the coconut from the taller tree reaches the ground with a speed \(V\) , what will be the speed (in terms of \(V\) ) of the coconut from the other tree when it reaches the ground? (b) If the coconut from the shorter tree takes time \(T\) to reach the ground, how long (in terms of \(T )\) will it take the other coconut to reach the ground?

Short Answer

Expert verified
(a) The speed is \(\frac{V}{\sqrt{2}}\). (b) The time is \(\sqrt{2} \times T\).

Step by step solution

01

Understand the problem

We have two coconuts falling from rest, with the first one falling from a tree twice as high as the second. We need to find out: (a) the relation of the final velocities with each other, and (b) the relation of the times taken to reach the ground.
02

Use the equations of motion

Since the coconuts fall freely from rest, we can use the equation: \ v_f^2 = v_i^2 + 2g h \ where \(v_f\) is final velocity, \(v_i\) is initial velocity (which is 0), \(g\) is acceleration due to gravity, and \(h\) is the height. Thus \(v_f = \sqrt{2gh}\).
03

Relate final speeds using given heights

For the taller tree, \(v_{f_T} = \sqrt{2g(2h)}\). For the shorter tree, \(v_{f_S} = \sqrt{2gh}\). Given \(v_{f_T} = V\), express \(v_{f_S}\) in terms of \(V\): \ v_{f_T} = \sqrt{2g \times 2h} = \sqrt{2} \times \sqrt{2gh} = \sqrt{2} \times v_{f_S} \ Therefore, \(v_{f_S} = \frac{V}{\sqrt{2}}\).
04

Understand time taken to fall

Using the equation \(t = \frac{v_f}{g}\), for the shorter tree \(t_S = \frac{\sqrt{2gh}}{g}\) and for the taller tree \(t_T = \frac{\sqrt{4gh}}{g}\).
05

Express longer time in terms of the shorter time

Since \(t_T = \frac{\sqrt{4gh}}{g}\) = \(\sqrt{2} \times \frac{\sqrt{2gh}}{g}\) = \(\sqrt{2} \times t_S\), then \(t_T = \sqrt{2} \times T\).

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Key Concepts

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

Equations of Motion
In understanding free fall motion, the equations of motion play a crucial role. They help describe the movement of objects under the influence of constant acceleration, such as gravity. When an object falls freely, it starts from rest, which means its initial velocity (\(v_i\)) is zero. Using the second equation of motion for velocity, we have:\[v_f^2 = v_i^2 + 2gh\]Here,
  • \(v_f\) is final velocity
  • \(h\) is the height from which the object falls
  • \(g\) stands for acceleration due to gravity
This equation is instrumental in finding the final velocities of the coconuts in this exercise. Given two coconuts falling from different heights, understanding the relationship between the final velocities and the heights becomes essential. With this equation, you can discern how high they fell from simply by comparing their speeds when they hit the ground.
Gravity
Gravity is the force that pulls objects towards the Earth's center. When discussing free fall, it's all about the influence of gravity acting on the falling objects. Gravity causes the objects to accelerate downwards at a constant rate, which on Earth is approximately 9.81 meters per second squared.

Since the coconuts fall freely with no other forces acting on them except gravity, it's essential to consider this constant acceleration. As they fall, their speed increases steadily due to gravity. The equation \(v_f = \sqrt{2gh}\) from the equations of motion illustrates gravity's role in determining the final velocity of the falling object.
  • It ensures objects gain speed as they descend.
  • It uniformly affects all free-falling objects irrespective of their mass.
Understanding gravity is key to solving problems involving free fall motion, like the one with the coconuts.
Velocity
Velocity in free fall motion describes the speed and direction of a falling object. In this exercise, since the coconuts are falling straight down, the direction is consistent, and we focus on the magnitude of the speed.

For an object starting from rest, the final velocity can be determined using the equation:\[v_f = \sqrt{2gh}\]This tells us how fast the object is moving just before it hits the ground.
  • The taller tree's coconut hits the ground faster due to having more height to accelerate through.
  • Conversely, the shorter tree's coconut has a lower speed, a relationship expressed in the solution as \(v_{f_S} = \frac{V}{\sqrt{2}}\).
Velocity is crucial in understanding how different factors like height affect the falling speed of objects in scenarios involving gravity.
Time of Descent
When objects fall freely under gravity, the time it takes to reach the ground is called the time of descent. Using the equation for time \[t = \frac{v_f}{g}\]you can determine how long an object remains in free fall.
  • For the shorter tree's coconut, its descent time is given as \(T\).
  • Because the taller tree is twice the height, its coconut takes longer, specifically \(t_T = \sqrt{2} \times T\).
This multiplicative factor of \(\sqrt{2}\) illustrates how increased height impacts descent time. A longer descent time implies more time for acceleration, resulting in a higher final speed. Understanding descent time is valuable for applications like predicting when a free-falling object will reach the ground. It highlights the role height plays in the dynamics of free fall motion.

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