Conservation Laws Homework help

In summary, the conversation is about a person seeking help with a physics homework question involving a car accelerating up a hill. They are given information about the mass, initial velocity, acceleration, distance, gravity, height, and work done by friction. After discussing the concept of energy conservation, they are instructed to calculate the final kinetic energy and change in potential energy of the car. They also question the significance of the 400J of work done by friction and seek clarification on the calculations.
  • #1
Lorax
42
0
Hi, I'm having a few problems with my Homework I'll post one question for now then if I find out where I got stuck I'll go on to my next question. Alright...

"A 1500kg car accelerates up a hill in an attempt to pass a semi truck, it had an initial velocity of 12m/s if accelerated at a rate of 2m/s^2 for the 180m up the slope. If the hill had a vertical height of 15m and ther was 400j of work done by the friction how much work was done by the cars engine?"

Alright, well I know the Mass, Vi, A, D, G, H, and Vf and the W done by the friction.

But I'm a little unsure about how to go about figuring this question out. If someone could start me off that would be great.
 
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  • #2
First of all, energy must be conserved (as you suggested). So, try to find an expression for the initial energy and the final energy.
 
  • #3
Hi,
The total energy of the system must be conserved, now at the start the car has velocity 12m/s and hence kinetic energy: 1/2mv^2. Since the change in the potential energy depends on CHANGE in height, assume it has initial height of zero, and so the total initial energy is: 1/2 m(12^2).
Now since acceleration is constant you can use
vf^2=vi^2 +2ad
Put your values into get vf, then u can get the final kinetic energy. Then calculate the change in potential energy: mg(15)
Now the final kintetic energy plus the potential energy, subtract 400J should equal the initial kinetic energy.
Hope that helps
 
  • #4
yeah thanks you two, I had figured out the final kinetic energy, and potential energy but was a biy unsure as to what to do with the 400j. Thanks! I'll add my next question in an hour or so.
 
  • #5
Actually now that I relooked over my answer that doesn't make any sense to me I get a number like 8687250-400. Can someone verify if what rayveld said is correct. Also if someone could maybe rewrite what he said that would be great help.
 
  • #6
Hi sorry if my last post was confusing i was in a rush. My answer to it came out as:
3,254,730 - 400=3,254,330 J
I don't know if its right but there should be a lot of work done by the car's engine to accelerate it at 2m/s.
 
  • #7
can someone verirify if rayveld has the right asnwer I did it and keep getting something different
 

FAQ: Conservation Laws Homework help

What are conservation laws?

Conservation laws are fundamental principles in physics that state certain physical quantities, such as energy, momentum, and angular momentum, are conserved or remain constant in a closed system. This means that these quantities cannot be created or destroyed, but can only be transferred or transformed.

Why are conservation laws important?

Conservation laws are important because they provide a framework for understanding and predicting the behavior of physical systems. They are fundamental principles that govern the behavior of matter and energy in the universe and are essential for many areas of physics, such as mechanics, thermodynamics, and electromagnetism.

What are the different types of conservation laws?

There are several types of conservation laws, including conservation of energy, conservation of momentum, conservation of angular momentum, and conservation of charge. These laws are based on different physical quantities and each has its own set of equations and principles.

How are conservation laws applied in real-world situations?

Conservation laws are applied in a wide range of real-world situations, from understanding the motion of objects to designing efficient energy systems. For example, the law of conservation of energy is used in calculating the trajectory of a projectile, while the law of conservation of momentum is used in designing rockets and spacecraft.

What are some common misconceptions about conservation laws?

One common misconception about conservation laws is that they only apply to closed systems. While they are most commonly used in closed systems, they can also be applied to open systems as long as all the inputs and outputs are accounted for. Another misconception is that conservation laws can be violated, when in fact they are fundamental principles that have been tested and proven to hold true in countless experiments.

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