Gravitational potential energy.

In summary, the boy on the sled has a gravitational potential energy of 24696 J at the top of the hill relative to the base. The sled moves at 9.8 m/s2 down the hill, and the work done by friction is 8750 J.
  • #1
cruisx
39
0

Homework Statement


Hey guys, just wondering if you guys could help me out a bit.

A boy on a sled with a total mass of 72kg slides from rest down a hill, which is 35m high. The friction force between sled and snow has a magnitude of 250N. If the slope of the hill makes an angle of 37 degrees with the horizontal, find:
a) the gravitational potential energy of the sled at the top of the hill relative to the base.

Homework Equations



If i am not mistaken the equation for Gav.pot energy is
U= GMe * m
...Re2

and the value of g can be found as g = G * Me/ (R + h)2

The Attempt at a Solution



I know i have the following from the question:

m= 72kg
h1=35m
Ff= 250N

now what i don't get is where the 37 degrees is supposed to come in and i am not quite sure that that is the equation that i am supposed to use. Could someone please explain to me how i would begin this question? I want to solve it my slef but can someone point me into a direction. thank you.edit: wait a second, i think i was doing it wrong. Would it be like E1g = mgh = (72kg)(9.8m/s2)(35m) = 24696 J ?
 
Last edited:
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  • #2
cruisx said:

Homework Equations



If i am not mistaken the equation for Gav.pot energy is
U= GMe * m
...Re2

and the value of g can be found as g = G * Me/ (R + h)2
Much simpler would be to use PE = mgh, which is perfectly good near the Earth's surface.


now what i don't get is where the 37 degrees is supposed to come in
Maybe you don't need it for part a. :wink:
 
  • #3
cruisx said:
edit: wait a second, i think i was doing it wrong. Would it be like E1g = mgh = (72kg)(9.8m/s2)(35m) = 24696 J ?
Now you've got it.
 
  • #4
Doc Al said:
Now you've got it.


Ok cool thanks guys, i think i can handle it form here ^_^. look like i will be studying all day for that physics test tomorrow :frown:
 
  • #5
Sorry for posting again but now i am stuck at part c of the question which is : the speed of the sled at the bottom of the hill.

How would i find this out? I know i have to use the 37 degrees somehow but i am stuck, I now have the following variables.

m=72kg
h1 = 35m
Ff = 250N
gav.pot energy : 24696J
Work: 8750J

Its been a while since i have had to find speed so a hint would be helpful =)
 
  • #6
What's the work done by friction? Hint: What's the distance traveled by the sled?

Set up an energy equation.
 

1. What is gravitational potential energy?

Gravitational potential energy is the energy an object possesses due to its position in a gravitational field. It is the energy that an object has because of its height above a reference point, such as the ground.

2. How is gravitational potential energy calculated?

The formula for calculating gravitational potential energy is PE = mgh, where PE is the potential energy, m is the mass of the object, g is the acceleration due to gravity, and h is the height of the object.

3. What factors affect gravitational potential energy?

The amount of gravitational potential energy an object has is affected by two main factors: the mass of the object and its height above the reference point. The greater the mass and the higher the object is, the more gravitational potential energy it will have.

4. Can gravitational potential energy be negative?

Yes, gravitational potential energy can be negative. This occurs when the reference point is set below the object, causing the height (h) in the formula to be negative. This negative potential energy indicates that the object is in a state of lower energy compared to its reference point.

5. What is the relationship between gravitational potential energy and kinetic energy?

Gravitational potential energy and kinetic energy are two forms of mechanical energy that are related to each other. When an object falls, its gravitational potential energy decreases as its kinetic energy increases. This is because the energy is being transferred from potential energy to kinetic energy. At the bottom of the fall, all of the potential energy has been converted into kinetic energy.

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