## yrelhan4 2 years ago Two blocks of masses m1=2kg and m2=5kg hang over a massless pulley as in the figure. A force F=100N acting on the axis of the pulley accelerates the system upward. Find : a) the acceleration of each block b) the tension in the string.

1. yrelhan4

2. yrelhan4

answer: 2 kg block accelerates 15.2 m/s^2 upward the 5 kg block accelerates .2 m/s^2 upward

3. yrelhan4

30/7 ? g=10m/s2

4. 3psilon

How would this problem be done with the force acting on the axis? that is new to me

5. yrelhan4

@3psilon it just means the system is pulled by a force upwards, i guess.

6. 3psilon

ok let me fool around with it and I'll see if I get that answer

7. yrelhan4

right!

8. 3psilon

So usually in an Atwell problem like this the acceleration is the same right? But I guess that force changes the acceleration of both?

9. yrelhan4

yes.. acceleration of both the blocks without the force is 30/7 m/s2 .. if that could help..

10. Vincent-Lyon.Fr

Actually, this problem is simpler than an Atwood machine. Since the pulley is massless, it is very easy to find the tension in the string, and the accelerations of M1 and M2.

11. yrelhan4

what about the force on the pulley?

12. Vincent-Lyon.Fr

Apply N's 2nd law to the pulley.

13. yrelhan4

the pulley is massless..

14. Vincent-Lyon.Fr

Makes it even easier!

15. Vincent-Lyon.Fr

If a massless body is accelerating, what will be the net force on it?

16. yrelhan4

0..

17. yrelhan4

@Vincent-Lyon.Fr what would i get after applying nlm to pulley?

18. Vincent-Lyon.Fr

Tension in the string... and the problem is done.

19. yrelhan4

i'll try .. i think i got it somewhat..

20. Vincent-Lyon.Fr

It is VERY easy, not joking!

21. yrelhan4

yeah.. thank you!