/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 31 A block with mass \(m=2.00 \math... [FREE SOLUTION] | 91Ó°ÊÓ

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A block with mass \(m=2.00 \mathrm{~kg}\) is placed against a spring on a frictionless incline with angle \(\theta=30.0^{\circ}\) (Fig. 8-44). (The block is not attached to the spring.) The spring, with spring constant \(k=19.6 \mathrm{~N} / \mathrm{cm},\) is compressed \(20.0 \mathrm{~cm}\) and then released. (a) What is the elastic potential energy of the compressed spring? (b) What is the change in the gravitational potential energy of the block- Earth system as the block moves from the release point to its highest point on the incline? (c) How far along the incline is the highest point from the release point?

Short Answer

Expert verified
(a) 39.2 J; (b) 39.2 J; (c) 4.00 m

Step by step solution

01

Convert Units

First, convert the spring constant from N/cm to N/m. Since there are 100 cm in a meter, we have \( k = 19.6 \, \text{N/cm} = 1960 \, \text{N/m} \). Also convert the compression distance from cm to meters: \( x = 20.0 \, \text{cm} = 0.20 \, \text{m} \).
02

Calculate Elastic Potential Energy

The elastic potential energy stored in the spring is given by the formula \( U_{\text{elastic}} = \frac{1}{2} k x^2 \). Substituting the known values, \( U_{\text{elastic}} = \frac{1}{2} \times 1960 \, \text{N/m} \times (0.20 \, \text{m})^2 = 39.2 \, \text{J} \).
03

Calculate Change in Gravitational Potential Energy

At the highest point on the incline, the gravitational potential energy is equal to the initial elastic potential energy because the system is frictionless and energy is conserved. Thus, the change in gravitational potential energy \( \Delta U_{\text{gravity}} \) is the same as \( U_{\text{elastic}} = 39.2 \, \text{J} \).
04

Calculate the Height Change

The change in gravitational potential energy can also be expressed as \( \Delta U_{\text{gravity}} = mgh \), where \( h \) is the vertical height. Rearranging gives \( h = \frac{\Delta U_{\text{gravity}}}{mg} = \frac{39.2 \, \text{J}}{2.00 \, \text{kg} \times 9.81 \, \text{m/s}^2} \approx 2.00 \, \text{m} \).
05

Calculate the Distance Along the Incline

Using the relation \( h = d \sin\theta \), where \( d \) is the distance along the incline, we solve for \( d \): \( d = \frac{h}{\sin(30.0^\circ)} = \frac{2.00 \, \text{m}}{0.5} = 4.00 \, \text{m} \).

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Key Concepts

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

Gravitational Potential Energy
Gravitational potential energy is an intriguing aspect of physics. It represents the energy an object has due to its position in a gravitational field, typically above the ground. In simpler terms, it is the energy stored in an object because of its height. The formula for calculating gravitational potential energy is \( U = mgh \), where:
  • \( m \) is the mass of the object
  • \( g \) is the acceleration due to gravity, approximately \( 9.81 \, \text{m/s}^2 \) on Earth
  • \( h \) is the height above a reference point
In scenarios where a spring launches an object up an incline, like in our example, the energy from the spring is converted into gravitational potential energy as the object ascends. As the object rises, it loses kinetic energy but gains gravitational potential energy, reflecting the energy change associated with height increase. Understanding these transfers can simplify tackling problems in mechanics by giving a clear view of how energy forms transform into one another.
Inclined Plane
An inclined plane is a flat surface tilted at an angle, other than horizontal. It helps in understanding how forces and energy affect objects on slopes. When a block is on a frictionless inclined plane, it moves under the action of gravity. The slope's angle \( \theta \) plays a significant role in determining the component forms of forces acting on the block.To find the distance the block travels along the incline, one must consider how this angle affects the forces and energy conversions. In our exercise, the block reaches a height \( h \) by traveling a distance \( d \) along the plane. The height is calculated using \( h = d \sin \theta \). This relationship links the vertical rise to the slanted path the block covers. When working with inclined planes, keep in mind the effects of the incline angle on motion and energy conversion.
Conservation of Energy
The law of conservation of energy is a cornerstone concept in physics, declaring that energy in an isolated system remains constant—it can neither be created nor destroyed. However, energy forms can convert into each other.In a frictionless system on an inclined plane, as in the exercise, we see elastic potential energy from the spring converting entirely into gravitational potential energy as the block rises to its highest point. The initial elastic potential energy is calculated using \( U_{\text{elastic}} = \frac{1}{2} k x^2 \), where \( k \) is the spring constant and \( x \) is the spring compression. Once the spring releases, this energy transforms as the block progresses upward.Examining such transformations within the laws of energy conservation broadens one's grasp of energy's behavior in physical systems, enabling resolution of complex problems involving motion, forces, and energy conversions.

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Most popular questions from this chapter

The surface of the continental United States has an area of about \(8 \times 10^{6} \mathrm{~km}^{2}\) and an average elevation of about \(500 \mathrm{~m}\) (above sea level). The average yearly rainfall is \(75 \mathrm{~cm} .\) The fraction of this rainwater that returns to the atmosphere by evaporation is \(\frac{2}{3} ;\) the rest eventually flows into the ocean. If the decrease in gravitational potential energy of the water-Earth system associated with that flow could be fully converted to electrical energy, what would be the average power? (The mass of \(1 \mathrm{~m}^{3}\) of water is \(1000 \mathrm{~kg} .)\)

A \(1.50 \mathrm{~kg}\) water balloon is shot straight up with an initial speed of \(3.00 \mathrm{~m} / \mathrm{s}\). (a) What is the kinetic energy of the balloon just as it is launched? (b) How much work does the gravitational force do on the balloon during the balloon's full ascent? (c) What is the change in the gravitational potential energy of the balloon-Earth system during the full ascent? (d) If the gravitational potential energy is taken to be zero at the launch point, what is its value when the balloon reaches its maximum height? (e) If, instead, the gravitational potential energy is taken to be zero at the maximum height, what is its value at the launch point? (f) What is the maximum height?

A 1500 kg car begins sliding down a \(5.0^{\circ}\) inclined road with a speed of \(30 \mathrm{~km} / \mathrm{h} .\) The engine is turned off, and the only forces acting on the car are a net frictional force from the road and the gravitational force. After the car has traveled \(50 \mathrm{~m}\) along the road, its speed is \(40 \mathrm{~km} / \mathrm{h} .\) (a) How much is the mechanical energy of the car reduced because of the net frictional force? (b) What is the magnitude of that net frictional force?

A \(15 \mathrm{~kg}\) block is accelerated at \(2.0 \mathrm{~m} / \mathrm{s}^{2}\) along a horizontal frictionless surface, with the speed increasing from \(10 \mathrm{~m} / \mathrm{s}\) to \(30 \mathrm{~m} / \mathrm{s} .\) What are \((\mathrm{a})\) the change in the block's mechanical energy and (b) the average rate at which energy is transferred to the block? What is the instantaneous rate of that transfer when the block's speed is (c) \(10 \mathrm{~m} / \mathrm{s}\) and (d) \(30 \mathrm{~m} / \mathrm{s} ?\)

A \(4.0 \mathrm{~kg}\) bundle starts up a \(30^{\circ}\) incline with \(128 \mathrm{~J}\) of kinetic energy. How far will it slide up the incline if the coefficient of kinetic friction between bundle and incline is \(0.30 ?\)

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