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Two blocks with masses of 4kg and 8kg

  • Thread starter pezzang
  • Start date
  • #1
29
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Two blocks with masses of 4kg and 8kg are connected by a string and slide down a 30 degree inclined plane. The coefficient of kinetic friction between 4kg block and the plane is 0.2; that between 8kg block and the palne is 0.35.
A) calculate the acceleration of each block.
b) calculate teh tension in the string
c) what happens if the positions of the blocks are reversed, so the 4kg block is above teh 8kg block?

picture

4kg ------- 8kg
the inclination goes up as it goes right so


8kg
------
---
4kg-

Like that.
I assumed that the acceleration of block a and b are teh same. can i assume that???? and i soloved it using ma equals w times sin30 - uwcos30 - T
and Ma = mg sin20 - .25 times mg cos30 - T

and so on,. I got 2.21 as the accelration. can anybody confirm and tell me how they got it? and for the rest too???
Thanks.
 
Last edited by a moderator:

Answers and Replies

  • #2
Chi Meson
Science Advisor
Homework Helper
1,789
10
THe accelerations would be the same in the first scenario, but this is the end result, not the initial assumption.

THe coefficients of friction are different, so one will drag more than the other.

THe force of friciton is equal to "mu" times the perpendicular componant of the weight (since that will be the magnitude of the normal force)

Find the net force that is parallel to the plane for both objects as a system, then divide that force by the total mass.

I got 0.718 m/s^2 as the acceleration
 
Last edited:

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