How high can it coast up the hill, if you neglect friction?

In summary, a 180 kg motorcycle traveling at 29 m/s with two 12 kg wheels with inner and outer radii of 0.280 m and 0.330 m, respectively, can coast up a hill with a height of 32 m if friction is neglected. The moment of inertia for the wheels needs to be calculated using 1/2 m (b^2 + a^2) and multiplied by 2. The velocity divided by the outer radius can be used to find the angular velocity. However, it is possible that the calculation was incorrect if the result is larger than the actual height of the hill. More information about the calculations would be necessary to determine where the mistake was made.
  • #1
alaa amed
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Homework Statement


Suppose a 180 kg motorcycle is heading toward a hill at a speed of 29 m/s. The two wheels weigh 12 kg each and are each annular rings with an inner radius of 0.280 m and an outer radius of 0.330 m.
How high can it coast up the hill, if you neglect friction in m?

*m = 180 kg
*v = 29 m/s
*h = 32 m

2. Homework Equations

mgh = 1/2 m v^2 + 1/2 I w^2

The Attempt at a Solution


First thing I did is finding the moment of inertia for the wheels, which is 1/2 m (b^2 + a^2) then I multiplied it by 2 since there are two wheels.

I then plugged that number for "I" in the above equation. I found w by dividing the given velocity by the outer radius(not sure if that is right) and then I had all the variables and solved for h but got an unreasonable number! bigger that the actual height of the hill.
 
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  • #2
alaa amed said:
I then plugged that number for "I" in the above equation. I found w by dividing the given velocity by the outer radius(not sure if that is right) and then I had all the variables and solved for h but got an unreasonable number! bigger that the actual height of the hill.
It's hard to be sure without seeing all your working, but it sounds like you only considered the wheels getting up the hill. Even then, I don't think you should have got an unreasonable answer. If you do not show you working we cannot tell where you went wrong.
 
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1. How does neglecting friction affect the coasting height up a hill?

Neglecting friction means that you are assuming there is no resistance or frictional force acting on the object as it moves up the hill. This can result in an overestimation of the coasting height as frictional forces can significantly impact an object's motion.

2. Is neglecting friction a realistic assumption?

No, neglecting friction is not a realistic assumption as it is almost impossible to completely eliminate friction in any real-world scenario.

3. What factors influence the coasting height up a hill?

The coasting height up a hill is influenced by various factors such as the mass and velocity of the object, the slope and length of the hill, and the presence of frictional forces.

4. How can we calculate the coasting height up a hill when neglecting friction?

To calculate the coasting height when neglecting friction, we can use the conservation of energy principle, which states that the total energy of a system remains constant. This means that the potential energy at the top of the hill is equal to the initial kinetic energy of the object.

5. Can we neglect friction in all scenarios when calculating coasting height?

No, it is not always appropriate to neglect friction when calculating the coasting height. In some cases, friction can significantly impact an object's motion and should be taken into consideration for more accurate calculations.

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