How Accurate Is the Calculated Friction Force for a Sled Sliding Down a Hill?

AI Thread Summary
The discussion focuses on calculating the average friction force for a sled sliding down a 500-meter slope with a height of 10 meters. The sled, weighing 60 kg, reaches a speed of 8 m/s at the bottom, leading to a calculated propulsive force of 480 N. However, the importance of the slope's height is questioned, as it has not been utilized in the calculations. Participants clarify the directions of forces involved, emphasizing that friction opposes the sled's motion while gravity acts downwards. The accuracy of the calculations and the relevance of height in determining friction are central to the conversation.
AlexPilk
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Homework Statement


The length of a slope is 500 meters and it's height is 10 meters. 60 kg sled went down the slope. Find the average friction force if it's speed in the end = 8 m/s (the starting speed = 0)

Homework Equations


Ft=mv-mv0
t=S/v

The Attempt at a Solution


Ft=mv-mv0=60*8=480
Average speed = (8+0)/2=4
t=500/4=125
F=480/125=3.84 N
Weight=mg=600
600-friction=3.84
friction=596.16 N

Is it correct?
 
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AlexPilk said:
F=480/125=3.84 N
Weight=mg=600
600-friction=3.84
You have calculated a propulsive force (F), right?
What direction does that act in?
What direction does mg act in?
(You might have noticed that you have not used the 10m height.)
 
haruspex said:
You have calculated a propulsive force (F), right?
What direction does that act in?
What direction does mg act in?
(You might have noticed that you have not used the 10m height.)
1.I think so, it's the force that accelerates the sled
2.Downwards
3. I do not really see use for the height of the slope

It looks like it makes sense, since I know the mass and acceleration I can calculate the overall force F, and friction works against mg, so the equation is correct, right?
 
AlexPilk said:
2.Downwards
As in vertically down? You obtained it by dividing momentum by time. What direction was the momentum in?
 

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