Several Energy Related Questions

  • Thread starter Fusilli_Jerry89
  • Start date
  • Tags
    Energy
In summary: I'm glad you didn't leave the answer in terms of "J"!In summary, the amount of work done by the force of gravity on the Earth when it moves in a circle about the sun is zero. In the second question, a force of 120N pushes a crate of mass 15kg at a constant speed of 3.2 m/s for a distance of 6.2m, generating 744J of heat energy. In the third question, the calculation for the amount of work done by the sun on the Earth is incorrect due to misunderstanding of the concept of work and the speed of the Earth. Lastly, in the fourth question, the force of friction on a car of mass 1350kg
  • #1
Fusilli_Jerry89
159
0

Homework Statement


1) If a planet moves in a circle about the sun, how much work does the force of gravity do on the earth? Give reasons for your answer.

2) A force of 120N pushes a crate mass 15kg along the ground at a constant speed of 3.2 m/s for a distance of 6.2m. What amount of heat energy was generated at this time?

3)The Earth has a mass of 5.98 x10^24 kg and a speed of 2.97 m/s. The sun, which is 1.49 x10^11m away, exerts 3.56 X10^11 N on it. If the Earth orbited the sun in a perfect circle, how much work would the sun do on the Earth in one second?

4) A car of mass 1350kg rolls from rest down a hill 235m long and 25m high. If its speed at the bottom of the hill is 12.0m/s, what's the force of friction on the car?


Homework Equations


Fnet=ma
pi*diameter
Ep=mgh
Ek=(0.5)mv^2

The Attempt at a Solution


1) I said none because the disatnce in the equation force times distance has to be a parallel distance to the force exerted on it, and its not in this case.

2)6.2m/3.2m/s=1.9375 sec
120N-Ff=m(0)
Ff=120N
W=Fd
W=120x6.2
W=744J

3)2(1.49 x10^11m)pi
d=2.97m
(3.56 x10^11 N)(2.97m)=1.06 x10^12 J

4)(1350kg)(9.8)(25m)
Ep'=330750 J
Ek2=(0.5)1350(144)=97200 J
W= 330750-97200=233550 J
233550J=235F
F=994N
 
Physics news on Phys.org
  • #2
Holy smokes. Your prof/TA is messing with you.

-1- right answer, wrong math. What does the phrase "gravity is a conservative force field" mean? Plus, what does the sun have to do with gravity on the Earth?

-3- The Earth has a speed of 2.97m/s with respect to what?
 
  • #3
If the Earth moves around in a circle, then there could not be any work done by the sun ! since the Earth's kinetic energy and potential energy stays constant.
 
  • #4
Fusilli_Jerry89 said:
1) I said none because the disatnce in the equation force times distance has to be a parallel distance to the force exerted on it, and its not in this case.
Good! The motion of the Earth is perpendicular to the direction of the sun's force--so no work is done.

2)6.2m/3.2m/s=1.9375 sec
120N-Ff=m(0)
Ff=120N
W=Fd
W=120x6.2
W=744J
I have no idea why you calculated the time, but the rest is correct.

3)2(1.49 x10^11m)pi
d=2.97m
(3.56 x10^11 N)(2.97m)=1.06 x10^12 J
What happened here? Review your answer for question 1. (FYI: What's that speed of 2.97m/s supposed to be? The speed of the Earth about the sun is about 10000 times greater.)

4)(1350kg)(9.8)(25m)
Ep'=330750 J
Ek2=(0.5)1350(144)=97200 J
W= 330750-97200=233550 J
233550J=235F
F=994N
Good.
 

1. What is renewable energy and why is it important?

Renewable energy is energy that comes from natural resources that can be replenished, such as sunlight, wind, and water. It is important because it reduces our reliance on fossil fuels and helps to reduce greenhouse gas emissions, which contribute to climate change. It also helps to diversify our energy sources and provides a more sustainable future for generations to come.

2. How do solar panels work?

Solar panels work by converting sunlight into electricity through the use of photovoltaic cells. These cells are made of layers of silicon, which create an electric field when exposed to sunlight. When sunlight hits the cells, it knocks electrons loose from the silicon atoms, creating a flow of electricity. This electricity can then be used to power homes, businesses, and other buildings.

3. What is the difference between renewable and non-renewable energy sources?

Renewable energy sources, such as solar, wind, and hydropower, are sources of energy that are naturally replenished and will not run out. Non-renewable energy sources, such as coal, oil, and natural gas, are finite resources that will eventually run out. They also produce harmful emissions that contribute to climate change.

4. How does energy consumption impact the environment?

Energy consumption has a significant impact on the environment. Burning fossil fuels for energy releases greenhouse gases, such as carbon dioxide, into the atmosphere, contributing to climate change. Extraction of fossil fuels also leads to environmental degradation and pollution. Additionally, the production and transportation of energy can have negative impacts on local ecosystems and wildlife.

5. What are some ways to reduce energy consumption?

There are several ways to reduce energy consumption, including using energy-efficient appliances and light bulbs, turning off lights and electronics when not in use, and using renewable energy sources. Conserving energy not only helps to reduce emissions and protect the environment, but it can also save individuals and businesses money on their energy bills.

Similar threads

Please help Work,power and energy question
    • Introductory Physics Homework Help
Replies
5
Views
2K

Hot Threads

Recent Insights

Back
Top