## TomLikesPhysics Group Title What forces act on the block with mass m2 (as seen on the picture)? Gravity for sure but I guess the cylinder does also something. Perhaps Tension plays also some role? one year ago one year ago

1. TomLikesPhysics Group Title

2. TomLikesPhysics Group Title

The cylinder can rotate without friction and is fixed there. The moment of inertia of the cylinder is 1/2*M1*R^2.

3. cheesesticks Group Title

gravity and friction

4. cheesesticks Group Title

tension is like tug of war

5. TomLikesPhysics Group Title

Sry, I forgot to mention that there is no friction.^^

6. cheesesticks Group Title

o is it multiple choice?

7. TomLikesPhysics Group Title

Nope :D

8. Vincent-Lyon.Fr Group Title

Weight, normal force, tension in the rope.

9. cheesesticks Group Title

WAIT THATS A ROPE?

10. mahmit2012 Group Title

|dw:1354312298270:dw|

11. Vincent-Lyon.Fr Group Title

That seems perfect!

12. mahmit2012 Group Title

|dw:1354312672595:dw|

13. TomLikesPhysics Group Title

Do you mean with T the Tension or Torque? If you mean Tension - why is T*R=I*alpha?

14. Vincent-Lyon.Fr Group Title

T is tension. Torque is: $$\large \tau\normalsize=TR$$

15. TomLikesPhysics Group Title

So the moment of inertia of the cylinder is connected with the tension... I have never seen this formula: T=I*alpha. Where does it come from? Normally Torque = Moment of Inertia * angular acceleration but now you say it also equals a force (tension)? I think the units do not add up because normally I*alpha gives you "Nm" and not "N".

16. shamim Group Title

$m _{2}gsin \theta -T=m _{2}a$

17. shamim Group Title

$R=m _{2}gcos \theta$

18. shamim Group Title

R is a force acted by the surface on the body of mass m2

19. Vincent-Lyon.Fr Group Title

I don't think anybody wrote : T=I*alpha, where T is a tension. This is dimensionnaly wrong. Equivalent of N's 2nd law for rotating bodies is: net torque $$\Large \tau$$ = $$I\;\alpha$$

20. Vincent-Lyon.Fr Group Title

@shamim careful, R is the radius of the pulley. The problem has already been solved by mahmit2012

21. shamim Group Title

ok

22. TomLikesPhysics Group Title

Ok, but why is T*R=I*alpha? I only saw this guy when T meant Torque so I have no clue where mahmit2012 got it from.

23. Vincent-Lyon.Fr Group Title

Because torque acting on the pulley is the moment of the force $$\vec T$$ about the axis of the pulley. Moment of $$\vec T$$ is simply $$RT$$ because $$\vec T$$ acts at right angles to the radius of the pulley.

24. TomLikesPhysics Group Title

Oh ... Torque = radius cross Force. Here the force on the cylinder is the tension. Also Torque equals moment of Inertia times alpha.

25. Vincent-Lyon.Fr Group Title

Exactly!

26. TomLikesPhysics Group Title

k, I think I get it now. Thanks a lot Vincent-Lycon.Fr and mahmit2012.

27. Vincent-Lyon.Fr Group Title

yw :)) goodbye!

28. TomLikesPhysics Group Title

A shame that I can not get you booth a "Best Response". mahmit2012 solved the thing but you (Vincent-Lyon.Fr) explained it further.

29. Vincent-Lyon.Fr Group Title

NP, mahmit deserves the award.