Find Coefficient of Kinetic Friction: Reasonable Assumptions

• mawalker
In summary, we are discussing assumptions that are reasonable to make in a scenario involving a sled on a slope. We are trying to find the coefficient of kinetic friction between the sled and the ground. Possible assumptions include treating the sled as a particle with constant acceleration, considering air resistance and thermal energy as negligible, and assuming that the force of friction is constant throughout the motion. However, some of these assumptions may not be accurate, as there is no mention of air resistance and thermal energy may actually be significant. It is also important to consider external forces acting on the system.
mawalker
ok i have a question about which assumptions which are allowable in this scenario.

A sled is being held at rest on a slope that makes an angle theta with the horizontal. After the sled is released, it slides a distance d1 down the slope and then covers the distance d2 along the horizontal terrain before stopping. Find the coefficient of kinetic friction Mu k between the sled and the ground if that coefficient is constant throughout the trip.

Which assumptions are reasonable to make

1. The sled can be treated as a particle moving with constant velocity (not necessarily the same velocity in both parts).

2. The sled can be treated as a particle moving with constant acceleration (not necessarily the same acceleration in both parts).

3. The sled cannot be treated as a particle.

4.The air resistance is significant to the problem.

5.The air resistance is negligible.

6.The amount of thermal energy generated is significant to the problem.

7.The amount of thermal energy generated is negligible.

8.The force of friction is constant throughout the motion.

9.The force of friction is different for different parts of the motion.

10.The sled is the only object in the system.

11.The sled and slope are both part of the system.

i said 5, air resistance is negligible since there is no mention of it... 3 therm energy is significant since it is mentioned, 8 friction is constant since that is given, and 11, the sled and slope are part of the system and it says that this is the wrong answer. Any ideas why?

well I would say 2 is reasonable too
and I don't agree that the thermal energy is significant

Last edited:
I dunno, that's still not covering everything...i'm not sure what I'm overlooking

mawalker said:
ok i have a question about which assumptions which are allowable in this scenario.

A sled is being held at rest on a slope that makes an angle theta with the horizontal. After the sled is released, it slides a distance d1 down the slope and then covers the distance d2 along the horizontal terrain before stopping. Find the coefficient of kinetic friction Mu k between the sled and the ground if that coefficient is constant throughout the trip.

Which assumptions are reasonable to make

1. The sled can be treated as a particle moving with constant velocity (not necessarily the same velocity in both parts). No

2. The sled can be treated as a particle moving with constant acceleration (not necessarily the same acceleration in both parts). Yes

3. The sled cannot be treated as a particle. It can

4.The air resistance is significant to the problem. No

5.The air resistance is negligible. Yes

6.The amount of thermal energy generated is significant to the problem. Yes, but you don't need to calulate it.

7.The amount of thermal energy generated is negligible. No

8.The force of friction is constant throughout the motion. No

9.The force of friction is different for different parts of the motion. Yes

10.The sled is the only object in the system. Yes, but there are external forces acting on the system that are known or determined by the geometry. You can argue all day about what the system is or is not, but since no questions were asked about what happens to anything beside the sled, the sled and the external forces acting onit are all you need.

11.The sled and slope are both part of the system. No

i said 5, air resistance is negligible since there is no mention of it... 3 therm energy is significant since it is mentioned, 8 friction is constant since that is given, and 11, the sled and slope are part of the system and it says that this is the wrong answer. Any ideas why?
View the white outs in the quote.

1. What is the coefficient of kinetic friction?

The coefficient of kinetic friction is a measure of the amount of friction between two surfaces in contact when one is in motion. It is represented by the symbol μk and is a dimensionless quantity.

2. How is the coefficient of kinetic friction determined?

The coefficient of kinetic friction can be determined experimentally by measuring the force required to keep an object in motion at a constant speed on a given surface. This force is then divided by the weight of the object to obtain the coefficient of kinetic friction.

3. What are some reasonable assumptions when finding the coefficient of kinetic friction?

Some reasonable assumptions when finding the coefficient of kinetic friction are that the surfaces in contact are flat and smooth, the objects are in constant motion, there is no air resistance, and the surfaces are not affected by external factors such as moisture or temperature.

4. How does the coefficient of kinetic friction affect the motion of objects?

The coefficient of kinetic friction plays a significant role in determining the motion of objects. Higher coefficients of kinetic friction result in more resistance to motion, making it more difficult for objects to slide or move along a surface.

5. What are some real-life applications of finding the coefficient of kinetic friction?

Finding the coefficient of kinetic friction is important in many real-life scenarios, such as designing brake systems for vehicles, determining the appropriate materials for tires, and calculating the force needed to move objects on different surfaces. It is also crucial in sports, such as determining the ideal playing surface for different sports and designing equipment with the right amount of grip.

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