Conservation of Energy question

In summary: The height is 500 m and the length is 300 m. So the hypotenuse is the length of the slide divided by the height of the slide. In summary, the rock has a kinetic energy of 340 kg when it slides down the hill.
  • #1
brittkub1291
24
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During a rockslide, a 340 kg rock slides from rest down a hillside that is 500 m long and 300 m high. The coefficient of kinetic friction between the rock and the hill surface is 0.24.

(a) If the gravitational potential energy U of the rock-Earth system is set to zero at the bottom of the hill, what is the value of U just before the slide?

(b) How much energy is transferred to thermal energy during the slide?

(c) What is the kinetic energy of the rock as it reaches the bottom of the hill?

(d) What is its speed then?

For letter a i found the gravitational potential energy using the formula Eg=mgy. This gave me 999600 J. I'm not sure how to find the thermal energy though, i thought that i could just multiply the gravitational energy by the coefficient of friction, but that didn't work.
 
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  • #2
Hi brittkub1291! :smile:
brittkub1291 said:
During a rockslide, a 340 kg rock slides from rest down a hillside that is 500 m long and 300 m high. The coefficient of kinetic friction between the rock and the hill surface is 0.24.
…
(b) How much energy is transferred to thermal energy during the slide?
…
I'm not sure how to find the thermal energy though, i thought that i could just multiply the gravitational energy by the coefficient of friction, but that didn't work.

Nooo … :frown:

Thermal energy is heat. What generates heat :rolleyes:? Friction! :rolleyes:

So the thermal energy is the work done by the friction force. :smile:
 
  • #3
Okay, i tried finding the friction force by using F=ma but i don't know if acceleration is constant or not.
 
  • #4
brittkub1291 said:
Okay, i tried finding the friction force by using F=ma but i don't know if acceleration is constant or not.

uhh?

Kinetic friction force = normal force times µk
 
  • #5
Yeah, i just realized that. So the normal force is mgcos(x), the friction force should just be (.24)(mgcos(x)) right? It keeps coming out wrong. When the question say the hill is 500 m long would that be the hypotenuse of the triangle? I was thinking that it wouldn't be..
 
  • #6
brittkub1291 said:
During a rockslide, a 340 kg rock slides from rest down a hillside that is 500 m long and 300 m high.

I don't see what else it can mean … high is vertically, so what can long be if it isn't the hypotenuse?
 
  • #7
Okay, i got it. I just was doing the problem as if they gave me the height and the length, and i used pathagoreans theorem to find the hypotenuse so it was making my answers wrong.
 

Related to Conservation of Energy question

1. What is the law of conservation of energy?

The law of conservation of energy states that energy cannot be created or destroyed, but can only be transferred or converted from one form to another. This means that the total amount of energy in a closed system remains constant over time.

2. Why is conservation of energy important?

Conservation of energy is important because it is a fundamental principle in science and has many practical applications. It helps us understand how energy moves and changes in different systems, and allows us to make predictions about the behavior of physical systems.

3. How is energy conserved in different forms?

In different systems, energy can be conserved in different forms. For example, in a closed mechanical system, energy can be conserved as kinetic energy or potential energy. In a closed chemical system, energy can be conserved as chemical energy. In any closed system, the total amount of energy remains the same.

4. Can energy ever be completely lost?

No, according to the law of conservation of energy, energy can never be completely lost. It may be converted into a form that is not easily usable, such as heat or sound, but it still exists in some form.

5. How does conservation of energy relate to sustainability?

Conservation of energy is closely related to sustainability because it emphasizes the importance of using energy resources efficiently and finding alternative, renewable sources of energy. By conserving energy, we can reduce our impact on the environment and help create a more sustainable future.

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