A challenging friction and forces question

  • Thread starter Thread starter hibachii
  • Start date Start date
  • Tags Tags
    Forces Friction
AI Thread Summary
The discussion revolves around a physics problem involving three connected masses and a pulley system, where the goal is to analyze forces, acceleration, and tension. Participants express confusion about setting up the equations of motion, particularly regarding the acceleration of each mass and the correct application of Newton's second law. It is emphasized that all masses share the same acceleration due to their connection via strings, despite potentially differing directions. The importance of drawing free-body diagrams for each mass is highlighted as a crucial step for solving the problem. Overall, the thread focuses on clarifying the approach to solving the dynamics of the system.
hibachii
Messages
17
Reaction score
0

Homework Statement



Three objects are connected on the table as shown in Figure P5.46 (a block of mass 1kg on a table is connected by two strings. The ends of the string each have a block hanging from it off the table, one of mass 4kg and one of mass 2kg. The strings are attached to a pulley system)
coefficient of kinetic friction between the block of mass m2
and the table is 0.350.
The objects have masses of m1
= 4.00 kg, m2
= 1.00 kg and m3
= 2.00 kg, and the
pulleys are frictionless. (a) Draw free-body diagrams of each of the objects. (b)
Determine the acceleration of each object and their directions. (c) Determine the
tensions in the two cords. What if? (d) If the tabletop were smooth, would the
tensions increase, decrease or stay the same? Explain.

Homework Equations



Figure P5.46 (in attachment)

The Attempt at a Solution



I have attempted a) and have no problem with it but it is b) and c) that is troubling me.
for b) i have written sum of all forces in the vertical direction is equal to 0(upwards positive). then i have input all the vertical forces for mass 1, T- mg=ma=0. I am stuck as i have two unknowns. please help!
 

Attachments

  • Untitled.png
    Untitled.png
    3.4 KB · Views: 788
Physics news on Phys.org
hibachii said:
for b) i have written sum of all forces in the vertical direction is equal to 0(upwards positive).
:confused:
then i have input all the vertical forces for mass 1, T- mg=ma=0. I am stuck as i have two unknowns.
Why are you setting the acceleration equal to zero?

Write separate force equations for each mass then solve together.
 
but then if i write separate force equations and solve together the acceleration would be the same for each mass wouldn't it? but it says to find acceleration of each mass. I am really confused :?
 
hibachii said:
but then if i write separate force equations and solve together the acceleration would be the same for each mass wouldn't it? but it says to find acceleration of each mass.
The masses are connected by the strings. They will all have the same acceleration (the same magnitude, but different directions, of course).
 
what are the force equations? i have no idea.
 
hibachii said:
what are the force equations? i have no idea.
Do the same thing you did for mass 1: Write equations expressing Newton's 2nd law. (Don't set the acceleration equal to zero, though.) Make sure you do part (a) first: you'll need to know the forces acting on each mass.
 
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 .
Thread 'Voltmeter readings for this circuit with switches'
TL;DR Summary: I would like to know the voltmeter readings on the two resistors separately in the picture in the following cases , When one of the keys is closed When both of them are opened (Knowing that the battery has negligible internal resistance) My thoughts for the first case , one of them must be 12 volt while the other is 0 The second case we'll I think both voltmeter readings should be 12 volt since they are both parallel to the battery and they involve the key within what the...
Back
Top