Prove conservation of energy

[hamid14]

Today we started on conservation of energy in physics and the teacher gave us a question. Using a ramp, it says prove that the total mechanical energy is conserved in the system. The marble (i havent measured the mass yet) is supposed to be rolled down the ramp and the height (delta H) is 1m. How would I prove that the energy is conserved and how would i find the velocity of the marble? Any help is appreciated.

[TerranceN]

To prove it you need to show that at two different times the energy is the same. The two ideal times will be when you let go of the marble and when the marble hits the ground. If you let h = 0 at the ground, then when you let go when the marble is at the top there will only be gravitational energy (because it is stationary, therefore no kinetic energy), and at the bottom there will only be kinetic energy (because it is at a relative height of 0, therefore no relative gravitational energy).

To measure the speed of the marble when it hits the ground you can use a kinematic equation.

d = (Vf - Vi) / 2 * t
or
Vf = 2d/t + Vi

You can measure the distance the marble falls (it's the length of the side of the ramp it rolls down), the time it takes, and Vi is zero, so you can find Vf.

I hope that helps.

[hamid14]

Wow TerranceN, thanks a lot man. That really helped! You really are a physics prof!

[TerranceN]

No I'm not.

I only kind of understand what is happening in my physics class (gr 12) at best. I honestly think the biggest jump in difficulty in high school is from gr 11 physics to gr 12 physics. For example, last week, we got our midterm exams back and about half of our class dropped, some of the people even had honours (80% or higher avg) last year.

My advice to you is to make sure you learn this stuff like the back of your hand, because it all compounds together. When you go into gr 12 physics, things like kinematics and conservation of energy will often be used as part of a newer, larger, concept.

For example, today we did a question about electric fields, a newer concept. It was an electron entering the area between two charged plates with a specified voltage, at a specified velocity parallel to the plates, and we had to find the final velocity when it exited the area between the plates. We had to use new stuff to find the force (and therefore acceleration), but then we had to use kinematics to find its final velocity.

The one really nice thing about gr 12 physics, is that it has made all my other courses seem easy in comparison.

And thanks for the compliment.

[hamid14]

But do I reallly need grade 12 physics for computer science?

[andrew.]

hamid14 @ Mon Nov 15, 2010 7:44 pm wrote:

But do I reallly need grade 12 physics for computer science?

I don't know, but I'd recommend taking physics. It gives you good problem solving skills, which are useful in any discipline.

[TheGuardian001]

Many universities require a science (other than the computer kind) for Computer Sciences. You probably don't specifically need to take physics though, some will also accept Bio or Chem.

[hamid14]

ok thats good to know, ill just take chemistry, since im getting a 90 something right now.