PHYS 1201W Chapter 6: chapter 6

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15 Oct 2016

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= we are looking at these in terms of mechanical systems. Conservation law - under certain conditions, the mechanical energy of a system is constant and is said to be conserved. Total energy = observed in nature: interchange of energy from one form to another yet sum of all energy remains the same. Energy may also be converted into matter & vice versa. Force f displaces an object along s, the work done by that force is the product of the force component and the displacement. Unit for work is joule (j) which is a newton meter. Work can be stated in term sof a product of 2 vectors called scalar / dot product. When work done by a force is negative, then the object is doing work on what is providing the force. If several forces are acting on an object, we can find their vector sum. Or we can calculate the work done by each force and sum.

Related Questions

Which of the following statement are true mechanical energy? Include all that apply.

1.The total amount of mechanical energy of an object is the sum of its potential energy and the kinetic energy.

2. Heat is a form of mechanical energy.

3. The mechanical energy of an object is always conserved.

4. When non-conservative forces do work, energy is transformed from kinetic to potential (or vice versa), but the total mechanical energy is conserved.

5. A bowling ball is mounted from a ceiling by way of a strong cable. It is a drawback and released, allowed to swing as a pendulum. As it swings from its highest position to its lowest position, the total mechanical energy is mostly conserved.

6. When a friction force does work on an object, the total mechanical energy of that object is changed.

7. The total mechanical energy of an object remains constant if the only forces doing work on the object are conservative forces.

8. If an object gains mechanical energy, then one can be certain that a non-conservative force is doing work.

is defined as $K=(1/2)mv^2$ . It seems reasonable to say that the speed of an object--and, therefore, its kinetic energy--can be changed by performing work on the object. In this problem, we will explore the mathematical relationship between the work done on an object and the change in the kinetic energy of that object.

Let us now consider the situation quantitatively. Let the mass of the sled be and the magnitude of the net force acting on the sled be. The sled starts from rest.

Consider an interval of time during which the sled covers a distance

and the speed of the sled increases from

. We will use this information to find the relationship between the work done by the net force (otherwise known as the network) and the change in the kinetic energy of the sled.

Find the net force

acting on the sled.

Express your answer in terms of someor all of the variables

, and

Find the net work

done on the sled.

Express your answer in terms of someor all of the variables

is defined as $K=(1/2)mv^2$ . It seems reasonable to say that the speed of anobject--and, therefore, its kinetic energy--can be changed byperforming work on the object. In this problem, we willexplore the mathematical relationship between the work done on anobject and the change in the kinetic energy of that object.

Let us now consider the situationquantitatively. Let the mass of the sled be and the magnitude of the net force acting on the sled be. The sled starts from rest.

Consider an interval of time duringwhich the sled covers a distance

and the speed of the sled increases from

. We will use this information to find the relationshipbetween the work done by the net force (otherwise known as thenet work) and the change in the kinetic energy of thesled.

Find the net force

acting on the sled.

Express your answer in terms of someor all of the variables

, and

Find the net work

done on the sled.

Express your answer in terms of someor all of the variables

and

graywildebeest386

A 270 g block is dropped onto a relaxed vertical spring that has aspring constant of k = 2.1 N/cm. The block becomes attached to thespring and compresses the spring 11 cm before momentarilystopping.
(a) While the spring is being compressed, what work is done on theblock by the gravitational force on it?
1Your answer is correct. J

(b) What work is done on the block by the spring force while thespring is being compressed?
2Your answer is incorrect. J

(c) What is the speed of the block just before it hits the spring?(Assume that friction is negligible.)
3Your answer is incorrect. m/s

(d) If the speed at impact is doubled, what is the maximumcompression of the spring?
4 m

Work done by a constant force is the dot product of the force andthe displacement. Work done by a variable force is calculated withan integral. The net work done on an object is equal to the changein the object's kinetic energy. If the object stops, its kineticenergy is zero.

PHYS 1201W Chapter 6: chapter 6

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