Gravitational potential energy homework

In summary, gravitational potential energy is the energy possessed by an object due to its position in a gravitational field. It is calculated using the formula PE = mgh and is measured in Joules (J). This energy affects an object's motion by converting into kinetic energy as the object falls. Gravitational potential energy can also be negative if the reference point for measuring height is chosen above the object.
  • #1
Erwin Schrodinger
24
0
A climber's gravitational potential energy increases from 14000J to 21000J while climbing a cliff. She expends 18000J of energy during this activity. What is the efficiency of this process?

A) 3%
B) 39%
C) 61%
D) 97%


Here is what I did.

Wpg = ∆Epg = Epg2-Epg1 = 21000-14000 = 7000J

% Eff = 100%(useful out)/total in = (100%)7000/18000 ≈ 39%


The answer key says it is 61% though. Is the answer key wrong or did I miss something?
 
Physics news on Phys.org
  • #2
I'd agree with your answer. They key must be wrong.
 
  • #3


Your calculation for the efficiency of the process is correct. The answer key must be incorrect. It is possible that the answer key is using a different formula or method to calculate efficiency, but based on the information given, your calculation is the most accurate. It is always important to double check answer keys and calculations to ensure accuracy.
 

1. What is gravitational potential energy?

Gravitational potential energy is the energy possessed by an object due to its position in a gravitational field. It is the energy that would be released if the object were to fall or move to a lower position within the field.

2. How is gravitational potential energy calculated?

Gravitational potential energy is calculated using the formula PE = mgh, where m is the mass of the object, g is the acceleration due to gravity, and h is the height or distance from the ground.

3. What are the units of gravitational potential energy?

The units of gravitational potential energy are Joules (J) in the SI system. However, it can also be expressed in other units such as calories or foot-pounds.

4. How does gravitational potential energy affect an object's motion?

Gravitational potential energy is a form of potential energy, which means it is stored energy that can be converted into other forms. When an object is at a higher position, it has more gravitational potential energy, and as it falls, this energy is converted into kinetic energy, which causes the object to accelerate.

5. Can gravitational potential energy be negative?

Yes, gravitational potential energy can be negative. This occurs when the reference point for measuring height is chosen above the object instead of below it. In this case, the gravitational potential energy is negative because the object has less potential energy than it would at the reference point.

Similar threads

Simple gravitational potential energy
    • Introductory Physics Homework Help
Replies
2
Views
957
Conservation of energy: Conceptual question
    • Introductory Physics Homework Help
Replies
9
Views
2K
What % of PEg must be converted in KE in order to double v?
    • Introductory Physics Homework Help
Replies
13
Views
2K
Solving a Physics Homework Problem: Work, Energy, and Conservation
    • Introductory Physics Homework Help
Replies
2
Views
2K
Gravitational Potential Energy Problem
    • Introductory Physics Homework Help
Replies
4
Views
3K
The Change In Gravitational Potential Energy?
    • Introductory Physics Homework Help
Replies
3
Views
5K
Conservation of energy/ efficiency question.
    • Introductory Physics Homework Help
Replies
7
Views
3K
When can the gravitational potential energy be zero?
    • Introductory Physics Homework Help
Replies
12
Views
4K

Hot Threads

Recent Insights

Back
Top