Kinetic Energy and Newton Forces - distance/speed

• Lori
In summary, the problem involves a sled with mass m and an initial speed of 2.20 m/s on a frozen pond with a coefficient of kinetic friction of 0.150. Using energy considerations, we can find the distance the sled moves before it stops by equating the work done by friction to the change in kinetic energy. This is because the work done by the applied force (the kick) is just for an instant and does not act beyond that. Therefore, the net work done is equal to the change in kinetic energy, which is negative for both the work done by friction and the change in kinetic energy.
Lori

Homework Statement

A sled of mass m is given a kick on a frozen pond. The kick imparts to it an initial speed of 2.20 m/s. The coefficient of kinetic friction between sled and ice is 0.150. Use energy considerations to find the distance the sled moves before it stops

Homework Equations

Friction Force = Friction coefficient * Normal Force
Normal Force = mass * g
W = KE = 1/2mv^2
W=fd

The Attempt at a Solution

So, I understand that force of friction is equal to mg*Friction coefficient (given that N=mg)

But, why is mgu=.5mv^2 (final Kinetic )

Shouldn't it be that the work is work done by applied force minus work done by Friction?

Why only look at friction work?

Lori said:
Shouldn't it be that the work is work done by applied force minus work done by Friction?
The work done by the applied force -- the kick -- is what gave the sled its initial velocity. It doesn't act beyond that. (The kick is just for an instant.)

Lori
Doc Al said:
The work done by the applied force -- the kick -- is what gave the sled its initial velocity. It doesn't act beyond that. (The kick is just for an instant.)
Oh ok, so all the work net is coming from the friction force which is equal to coefficient friction * mass *gravity * distance. And, since work net is equal to total kinetic energy which is just .5mv^2, we set those equal to each other.

Lori said:
Oh ok, so all the work net is coming from the friction force which is equal to coefficient friction * mass *gravity * distance. And, since work net is equal to total kinetic energy which is just .5mv^2, we set those equal to each other.
Right. Another way to word it: The net work done equals the change in KE. (Both the work done by friction and the change in KE are negative.)

Lori

1. What is kinetic energy?

Kinetic energy is the energy an object possesses due to its motion. It is dependent on the mass and velocity of the object, and can be calculated using the equation KE = 1/2 * m * v^2, where m is the mass of the object and v is its velocity.

2. How does kinetic energy relate to Newton's laws of motion?

According to Newton's second law of motion, the net force acting on an object is equal to its mass multiplied by its acceleration. Since kinetic energy is directly proportional to an object's mass and the square of its velocity, it is also related to the force acting on the object. This means that as an object's kinetic energy increases, so does the force acting on it.

3. How does distance affect kinetic energy?

The distance an object travels does not directly affect its kinetic energy. However, the distance over which the object accelerates can affect its final kinetic energy. For example, if an object is accelerating over a longer distance, it will have a greater final velocity and therefore a greater kinetic energy.

4. How does speed affect kinetic energy?

Speed is a crucial factor in determining an object's kinetic energy. Since kinetic energy is directly proportional to the square of an object's velocity, a small increase in speed can result in a significant increase in kinetic energy. This is why objects moving at high speeds, such as a bullet, possess a large amount of kinetic energy.

5. What are some real-life examples of kinetic energy and Newton's laws?

Some real-life examples of kinetic energy and Newton's laws include a bouncing ball (demonstrating Newton's laws of motion), a car moving at a high speed (possessing a large amount of kinetic energy), and a roller coaster (demonstrating the relationship between kinetic energy and distance/speed).

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