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A ball is thrown upward with an initial velocity of \(15 \mathrm{~m} / \mathrm{s}\) at an angle of \(60.0^{\circ}\) above the horizontal. Use energy conservation to find the ball's greatest height above the ground.

Short Answer

Expert verified
The ball reaches a maximum height of 8.57 meters.

Step by step solution

01

Define the system and known values

We have a ball thrown with an initial speed of \(v_i = 15\, \mathrm{m/s}\) at an angle \(\theta = 60.0^\circ\) above the horizontal. We need to find the maximum height it reaches using the conservation of energy principles.
02

Resolve initial velocity into components

The initial velocity can be split into horizontal and vertical components. The vertical component of velocity is calculated as:\[ v_{iy} = v_i \cdot \sin(\theta) = 15 \cdot \sin(60^\circ) = 15 \times \frac{\sqrt{3}}{2} = 15 \times 0.866 = 12.99 \, \mathrm{m/s} \]
03

Apply conservation of mechanical energy

At the maximum height, all vertical kinetic energy is converted into potential energy. Using energy conservation: \[ \frac{1}{2} m v_{iy}^2 = mgh \] where \( h \) is the height, \( m \) is the mass of the ball, and \( g = 9.81\, \mathrm{m/s^2} \) is the acceleration due to gravity. The mass \( m \) will cancel out.
04

Solve for the maximum height

Plug in the values into the equation:\[ \frac{1}{2} \times 12.99^2 = 9.81 \times h \]Solve for \( h \):\[ h = \frac{12.99^2}{2 \times 9.81} = \frac{168.08}{19.62} = 8.57 \, \mathrm{m} \]
05

Verify calculations

Double-check calculations for errors. Confirm that the trigonometric values and arithmetic are correct. The calculations match, affirming that the maximum height reached by the ball is 8.57 meters.

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Key Concepts

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

Projectile Motion
Projectile motion occurs when an object is thrown into the air and moves under the influence of gravity. This type of motion has both horizontal and vertical components. For example, when a ball is thrown upward at an angle, it travels along a curved path. Understanding projectile motion is essential for solving problems like finding the maximum height the ball reaches or how far it travels.

This kind of motion can be analyzed by splitting the velocity into two components:
  • **Horizontal Component**: This remains constant because no external horizontal forces are acting on the projectile (neglecting air resistance).
  • **Vertical Component**: This is affected by gravity, causing the projectile to slow down as it ascends and speed up as it descends.
Understanding these components helps in applying the right physics principles, like conservation of energy, to track the motion and solve for unknowns like maximum height or range.
Kinematic Equations
Kinematic equations are a set of formulas used to describe the motion of objects. These equations are particularly useful for solving problems in projectile motion, as they relate different quantities like displacement, velocity, and time.

For example, the vertical component of velocity in projectile motion can be found using:
  • \( v_{iy} = v_i \cdot \sin(\theta) \)
This helps determine how high the projectile will go. When you combine the initial speed with the angle of launch, you can solve for distinct vertical and horizontal movements.

Other kinematic equations help predict outcomes, such as when an object will hit the ground or reach its peak height. Familiarity with these equations aids in solving energy conservation problems effectively.
Mechanical Energy
Mechanical energy is the sum of kinetic energy and potential energy within a system. In the context of projectile motion, the conservation of mechanical energy principle states that the total mechanical energy remains constant if only conservative forces like gravity act on the object.

At the maximum height of a projectile, its vertical kinetic energy has been completely converted to potential energy. This can be represented as:
  • \( \frac{1}{2} m v_{iy}^2 = mgh \)
The mass of the object cancels out, simplifying the calculations and making it easier to solve for unknown variables like the maximum height. Understanding mechanical energy conservation is critical for predicting how energy transforms during the projectile's flight.
Motion in Two Dimensions
Motion in two dimensions involves objects moving in a plane, having both vertical and horizontal components. This is more complex than one-dimensional motion because it requires analyzing two directions simultaneously.

For projectiles, the key is to consider:
  • **Vertical Movement**: Affected by gravity. Initial vertical velocity can be calculated using the angle and is essential for finding the maximum height.
  • **Horizontal Movement**: Constant velocity assuming no air resistance, crucial for calculating the range.
By breaking down the motion into these components, equations of motion can be independently applied in vertical and horizontal directions. This enables precise predictions about the object’s path and position throughout its journey, leading to solutions for practical problems like determining height or travel distance.

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Most popular questions from this chapter

II A slingshot obeying Hooke's law is used to launch pebbles vertically into the air. You observe that if you pull a pebble back \(20.0 \mathrm{~cm}\) against the elastic band, the pebble goes \(6.0 \mathrm{~m}\) high. (a) Assuming that air drag is negligible, how high will the pebble go if you pull it back \(40.0 \mathrm{~cm}\) instead? (b) How far must you pull it back so it will reach \(12.0 \mathrm{~m} ?\) (c) If you pull a pebble that is twice as heavy back \(20.0 \mathrm{~cm},\) how high will it \(\mathrm{go} ?\)

Fleas are agile, wingless insects that feed on the blood of their hosts. Although they are typically \(2-3 \mathrm{~mm}\) long with a mass of \(4.5 \times 10^{-4} \mathrm{~kg},\) they have an astonishing ability to jump when threatened. Their propulsion, which can briefly produce accelerations more than 100 times that of gravity, comes not from muscles but, in fact, from an elastomeric protein called resilin, which acts as a spring. Given that the typical launch velocity of a flea is about \(1 \mathrm{~m} / \mathrm{s},\) what total energy must be stored in the resilin just before the flea jumps?

Pendulum. A small \(0.12 \mathrm{~kg}\) metal ball is tied to a very light (essentially massless) string that is \(0.8 \mathrm{~m}\) long. The string is attached to the ceiling so as to form a pendulum. The pendulum is set into motion by releasing it from rest at an angle of \(60^{\circ}\) with the vertical. (a) What is the speed of the ball when it reaches the bottom of the arc? (b) What is the centripetal acceleration of the ball at this point? (c) What is the tension in the string at this point?

A \(2.50 \mathrm{~kg}\) mass is pushed against a horizontal spring of force constant \(25.0 \mathrm{~N} / \mathrm{cm}\) on a frictionless air table. The spring is attached to the tabletop, and the mass is not attached to the spring in any way. When the spring has been compressed enough to store \(11.5 \mathrm{~J}\) of potential energy, the mass is suddenly released from rest. (a) Find the greatest speed the mass reaches. When does this occur? (b) What is the greatest acceleration of the mass, and when does it occur?

The power of the human heart. The human heart is a powerful and extremely reliable pump. Each day it takes in and discharges about \(7500 \mathrm{~L}\) of blood. Assume that the work done by the heart is equal to the work required to lift that amount of blood a height equal to that of the average American female, approximately \(1.63 \mathrm{~m} .\) The density of blood is \(1050 \mathrm{~kg} / \mathrm{m}^{3} .\) (a) How much work does the heart do in a day? (b) What is the heart's power output in watts? (c) In fact, the heart puts out more power than you found in part (b). Why? What other forms of energy does it give the blood?

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