Help with Forces, Friction and Negative Velocity

AI Thread Summary
The discussion focuses on seeking help with problems related to forces, friction, and negative velocity, particularly due to a lack of prior instruction from the professor. The first question involves calculating the angle of elevation for a track based on the thickness of elevation blocks. The second question requires drawing a free-body diagram for a block sliding down an inclined plane, taking into account friction, weight, and normal force. The third question asks for the calculation of average velocity over specified time intervals and the interpretation of negative average velocity. Participants are encouraged to share their progress and clarify their understanding of the concepts involved.
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I tried doing these but my professor has not gone over forces yet. I tried using the book, but I got stuck on these questions. Please help.

1) Two calibrated elevation blocks have a combined thickness of 1.86 cm. Find the angle of elevation of the 1.00-meter long track for this situation.

2) A block having mass M slides down an inclined plane. THe force of friction between the plane and the inclined plane is f , the block's weight is Mg and the normal force is N . Draw a freebody force diagram showing the forces acting on the block.

3) For the following position versus time values, calculate the average velocity for each of the four time intervals. What is the physical meaning of a negative average velcity?
Position (m) 1.24, 1.57, 2.63, 2.25, 2.00
Time (s) 1.00, 1.74, 2.33, 2.70, 3.00
 
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Please show us what you have got so far.
 
The problem is that I don't know where to start and what formula to use.
 
Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
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