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A 47.0-g golf ball is driven from the tee with an initial speed of \(52.0 \mathrm{m} / \mathrm{s}\) and rises to a height of \(24.6 \mathrm{m} .\) (a) Neglect air resistance and determine the kinetic energy of the ball at its highest point. (b) What is its speed when it is \(8.0 \mathrm{m}\) below its highest point?

Short Answer

Expert verified
The kinetic energy at the highest point is 52.421 J. The speed 8.0 m below its highest point is 52.9 m/s.

Step by step solution

01

Calculate Initial Kinetic Energy

First, we use the formula for kinetic energy to find the initial kinetic energy of the ball right after it's hit: \[ KE_i = \frac{1}{2} m v_i^2 \]where \(m = 0.047\, \text{kg}\) (converted from grams) and \(v_i = 52.0\, \text{m/s}\). Calculate: \[ KE_i = \frac{1}{2} \times 0.047 \times (52.0)^2 = 63.752\, \text{J}\].
02

Calculate Potential Energy at Highest Point

At its highest point, the golf ball has converted some of its kinetic energy into potential energy. The potential energy at the highest point can be found with: \[ PE_{top} = mgh \] where \(h = 24.6\, \text{m}\) and \(g = 9.81\, \text{m/s}^2\). Calculate: \[ PE_{top} = 0.047 \times 9.81 \times 24.6 = 11.331\, \text{J} \].
03

Determine Kinetic Energy at Highest Point

At the highest point, the remaining kinetic energy (\[ KE_{top} \]) is the initial kinetic energy minus the potential energy at the highest point: \[ KE_{top} = KE_i - PE_{top} \] \[ KE_{top} = 63.752 - 11.331 = 52.421\, \text{J} \].
04

Calculate Speed at 8.0m Below Highest Point

To find the speed when the ball is 8.0 m below its highest point, first find the potential energy at that point: New height \( h' = 24.6 - 8.0 = 16.6 \text{m} \)\[ PE' = mgh' = 0.047 \times 9.81 \times 16.6 = 7.678\, \text{J} \]Now use the conservation of energy to find the kinetic energy: \[ KE' = KE_i - PE' = 63.752 - 7.678 = 56.074\, \text{J} \]Use the kinetic energy to solve for speed: \[ \frac{1}{2} m v'^2 = KE' \]\[ v' = \sqrt{\frac{2 \times 56.074}{0.047}} = 52.9\, \text{m/s} \].

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Key Concepts

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

Potential Energy
Potential energy is a fundamental concept in physics that represents the energy stored in an object due to its position in a force field, most commonly the gravitational field of the Earth. In the context of projectile motion, such as the motion of a golf ball being hit from a tee, potential energy plays a crucial role in understanding how energy is transformed.When the golf ball reaches its highest point, its gravitational potential energy is at its maximum. This is calculated using the formula: \[ PE = mgh \]where \( m \) is the mass of the object (0.047 kg for the golf ball), \( g \) is the acceleration due to gravity (9.81 m/s²), and \( h \) is the height above the reference point (24.6 m in our original problem). This energy represents the potential for the ball to do work as it moves back to Earth, converting potential energy back into kinetic energy as it falls.
Conservation of Energy
The principle of conservation of energy tells us that in a closed system, the total energy remains constant over time. This means energy cannot be created or destroyed, only transformed from one form to another.For the golf ball, the total mechanical energy at any point during its motion is the sum of its kinetic and potential energies. Initially, when the ball is hit, it has maximum kinetic energy and minimal potential energy. As the ball rises, kinetic energy is gradually transformed into potential energy until it reaches the highest point of its trajectory. Here, it has maximum potential energy and less kinetic energy.The equation representing this transformation is:\[ KE_i + PE_i = KE + PE \]Understanding this energy transformation is key to solving problems where we need to find the ball's speed at different points in its motion, such as when it is at a different height than its highest point.
Projectile Motion
Projectile motion is a form of motion experienced by an object that is projected into the air and influenced only by gravity. It is important to ignore any air resistance for a straightforward analysis, as in our example with the golf ball. The motion can be separated into two components: vertical and horizontal. The vertical motion is influenced by gravity, affecting the projectile's height and contributing to changes between kinetic and potential energy. The horizontal component remains constant as no external forces are acting horizontally (assuming no air resistance). Understanding projectile motion involves calculating the positions and velocities at different points in time. In our problem, to determine the ball's speed 8 meters below its highest point, we need to factor in how potential energy changes as the ball drops and converts back to kinetic energy. The formulas show how energy transformation impacts the motion and speed, providing insight into how fast and at what altitude the projectile moves during its trajectory.

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Most popular questions from this chapter

A 67.0 -kg person jumps from rest off a \(3.00-\mathrm{m}\) -high tower straight down into the water. Neglect air resistance. She comes to rest \(1.10 \mathrm{m}\) under the surface of the water. Determine the magnitude of the average force that the water exerts on the diver. This force is nonconservative.

A husband and wife take turns pulling their child in a wagon along a horizontal sidewalk. Each exerts a constant force and pulls the wagon through the same displacement. They do the same amount of work, but the husband's pulling force is directed \(58^{\circ}\) above the horizontal, and the wife's pulling force is directed \(38^{\circ}\) above the horizontal. The husband pulls with a force whose magnitude is \(67 \mathrm{N}\). What is the magnitude of the pulling force exerted by his wife?

The motor of a ski boat generates an average power of \(7.50 \times 10^{4} \mathrm{W}\) when the boat is moving at a constant speed of \(12 \mathrm{m} / \mathrm{s}\) When the boat is pulling a skier at the same speed, the engine must generate an average power of \(8.30 \times 10^{4}\) W. What is the tension in the tow rope that is pulling the skier?

A 2.00-kg rock is released from rest at a height of 20.0 m. Ignore air resistance and determine the kinetic energy, gravitational potential energy, and total mechanical energy at each of the following heights: \(20.0,10.0,\) and \(0 \mathrm{m}\)

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