Newton's law problem have attempted it

  • Thread starter Thread starter thugg
  • Start date Start date
  • Tags Tags
    Law Newton's law
Click For Summary

Homework Help Overview

The discussion revolves around a problem related to Newton's laws of motion, specifically involving tensions in ropes and the forces acting on blocks of different masses. The original poster attempts to calculate the tension in the ropes connecting the blocks but encounters a discrepancy between their calculated values and the answer provided in the textbook.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster outlines their calculations for the tensions and acceleration, while some participants question the accuracy of the equations used, particularly regarding the forces acting on the 40 kg block.

Discussion Status

Participants are actively engaging with the problem, with one providing feedback on a potential mistake in the original poster's approach. There is an acknowledgment of the need to reconsider the forces acting on the blocks, indicating a productive direction in the discussion.

Contextual Notes

The problem involves assumptions about negligible mass and frictionless conditions, which are relevant to the calculations being discussed. The original poster's confusion about the correct tension values suggests a need for clarity on the forces involved.

thugg
Messages
9
Reaction score
0
Newton's law problem...have attempted it

http://img128.imageshack.us/img128/2941/asd6rh.jpg

rope is of negligible mass and no friction...now this is what i did

the bc and ab are subscripts for cords between each block

9.8(10)- Tbc = 10a
9.8(40)-Tab = 40a
Tab=30a

so by substituting i get a =5.6

then i plug it into get Tbc...which gives me 42N.

but the answer in the book says 36.8N...dunno what I am doing wrong, any ideas?
 
Last edited by a moderator:
Physics news on Phys.org
thugg said:
9.8(10)- Tbc = 10a

This is OK.

9.8(40)-Tab = 40a

This is not OK.

You've got the weight of the 40 kg block and the tension pulling upwards, which is good. But Tbc is also acting on the 40 kg block, and you've left that out.

That's the only mistake I see, so that should fix the problem.
 
And I've deleted your identical thread in the K-12 HW Forum. Please do not post multiple threads for the same topic.
 
wow can't believe i didnt think of that...weird
 

Similar threads

Newton's law problem: Helicopter lifting a box with a rope
  • · Replies 5 ·
Replies
5
Views
3K
Two Questions on Newton Law Problems
  • · Replies 5 ·
Replies
5
Views
3K
Newton's Third Law Problem: Two masses, a rope and a pulley
  • · Replies 21 ·
Replies
21
Views
11K
Newton's Laws Homework question: Double incline mass problem
  • · Replies 4 ·
Replies
4
Views
2K
Problem of spring block system: force vs conservation of energy
  • · Replies 20 ·
Replies
20
Views
4K
What is the Tension and Acceleration in Newton's Law of a Sled Problem?
  • · Replies 3 ·
Replies
3
Views
3K
Newton's law problem on homogeneous flexible rope
  • · Replies 2 ·
Replies
2
Views
2K
Using conservation of energy vs. Newton's laws in a pulley problem
  • · Replies 7 ·
Replies
7
Views
2K
Question Pertaining To Newton's Laws
  • · Replies 20 ·
Replies
20
Views
4K
Action reaction problem or Newton's 3 law
  • · Replies 8 ·
Replies
8
Views
2K