# Reasonable assumptions

1. Nov 1, 2006

### 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?

2. Nov 1, 2006

### *best&sweetest*

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

Last edited: Nov 1, 2006
3. Nov 1, 2006

### mawalker

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

4. Nov 2, 2006

### OlderDan

View the white outs in the quote.