Find Coefficient of Kinetic Friction: Reasonable Assumptions

[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?

 

[*best&sweetest*]

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

 

[mawalker]

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

 

[OlderDan]

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?

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