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CP A 4.80 -kg bucket of water is accelerated upward by a cord of negligible mass whose breaking strength is 75.0 \(\mathrm{N}\) . If the bucket starts from rest, what is the minimum time required to raise the bucket a vertical distance of 12.0 \(\mathrm{m}\) without breaking the cord?

Short Answer

Expert verified
The minimum time required is approximately 2.03 seconds.

Step by step solution

01

Find the gravitational force acting on the bucket

The gravitational force \( F_g \) is given by \( F_g = m \cdot g \) , where \( m = 4.80 \, \text{kg} \) is the mass of the bucket and \( g = 9.80 \, \text{m/s}^2 \) is the acceleration due to gravity. Substituting these values, \( F_g = 4.80 \, \text{kg} \times 9.80 \, \text{m/s}^2 = 47.04 \, \text{N}\).
02

Calculate the maximum net force without breaking the cord

The maximum force the cord can withstand is 75.0 N. To find the maximum net force \( F_{net} \) that can be applied upward, subtract the gravitational force from this: \( F_{net} = 75.0 \, \text{N} - 47.04 \, \text{N} = 27.96 \, \text{N} \).
03

Determine the maximum acceleration

The net force is also given by \( F_{net} = m \cdot a \). Solving for acceleration \( a \), we have: \[ 27.96 \, \text{N} = 4.80 \, \text{kg} \cdot a \]\[ a = \frac{27.96 \, \text{N}}{4.80 \, \text{kg}} \approx 5.83 \, \text{m/s}^2 \].
04

Use kinematic equations to find the time

The bucket starts from rest, so initial velocity \( u = 0 \), and we want to cover a distance \( s = 12.0 \, \text{m} \). Use the equation: \[ s = ut + \frac{1}{2}at^2 \]\[ 12.0 = 0 + \frac{1}{2} \times 5.83 \times t^2 \]Solving for \( t \), we get:\[ 12.0 = 2.915t^2 \]\[ t^2 = \frac{12.0}{2.915} \approx 4.116 \]\[ t \approx \sqrt{4.116} \approx 2.03 \, \text{s} \].

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Key Concepts

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

Newton's Laws of Motion
Newton's Laws of Motion serve as the building blocks for understanding how objects behave when forces act upon them. In our exercise, these laws help us decipher the movement of the bucket.

1. **First Law (Law of Inertia):** This law states that an object at rest will stay at rest, and an object in motion will stay in motion unless acted upon by a net external force. In the case of the bucket, it starts from rest and only begins to move when the upward force is applied.

2. **Second Law (Law of Acceleration):** This law describes how the acceleration of an object depends on two variables - the net force acting upon the object and the object's mass. It is represented by the equation: \( F_{net}=m\cdot a \). Here, we first calculate the net force that the cord can handle, considering the force needed to overcome gravity. Then, we determined the resulting acceleration.

3. **Third Law (Action and Reaction):** For every action, there is an equal and opposite reaction. Though not directly calculated in this exercise, this principle is what allows the cord to exert an upward force on the bucket while the bucket pulls downward on the cord.
Kinematics
Kinematics is all about describing motion using mathematical equations, without necessarily considering the forces causing such motion. In this particular problem, we compute the time it takes for the bucket to travel a certain distance upwards starting from rest.

Using the kinematic equation \( s = ut + \frac{1}{2}at^2 \), we can determine how long it takes to raise the bucket 12 meters. Since the bucket starts from rest, its initial velocity \( u \) is zero, simplifying the equation to focus on distance \( s \), acceleration \( a \), and time \( t \).

By rearranging and solving \( 12.0 = 0 + \frac{1}{2} \cdot 5.83 \cdot t^2 \), we find the time \( t \) which is approximately 2.03 seconds. This kinematic approach allows us to link motion to time and acceleration.
Forces and Motion
In the realm of physics, understanding the relationship between forces and motion is crucial. Forces are vectors, meaning they have both magnitude and direction, and are responsible for changes in the state of motion of objects.

In our exercise, the forces involved include the gravitational force pulling the bucket downward and the tension force from the cord pulling it upward. By computing the gravitational force as \( F_g = 47.04 \, N \) and knowing the maximum tension the cord can withstand is 75.0 N, we determine the net force that is effectively used to accelerate the bucket upward. This net force (27.96 N) leads to our calculated acceleration, as derived using Newton's second law.

The concept of forces and motion helps connect the physical interaction (forces) with observable effects (motion) and allows us to predict the outcome - like calculating how long it takes to lift the bucket without exceeding the cord's breaking strength.
Dynamics of Circular Motion
While not directly involved in linear motion problems like our exercise, the dynamics of circular motion provide insights into how forces guide objects along curved paths. It involves additional considerations such as centripetal force, which acts perpendicular to the direction of motion.

However, understanding circular motion dynamics can still enrich our understanding of motion under constraint forces, like tension in a cord. Even though a bucket moving vertically in this problem does not imply circular dynamics, any scenario involving objects swinging or rotating would require such an analysis. Forces in circular motion ensure the consistency of speed along the curve, all while maintaining the path.

This knowledge helps when transitioning from purely linear problems to those where an object might move in loops or spirals, necessitating an understanding of angular velocity, centripetal force, and other factors that influence circular motion.

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Most popular questions from this chapter

World-class sprinters can accelerate out of the starting blocks with an acceleration that is nearly horizontal and has magnitude 15 \(\mathrm{m} / \mathrm{s}^{2}\) . How much horizontal force must a 55 -kg sprinter exert on the starting blocks during a start to produce this acceleration? Which body exerts the force that propels the sprinter: the blocks or the sprinter herself?

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