# Tension in the string and tangential accleration

Tags:
1. Aug 31, 2015

### Hamza Abbasi

1. The problem statement, all variables and given/known data
A particle of mass m is whirled on the end of a string of length R. The motion is in vertical plane in Earth's gravitational field . The instantaneous speed is v when the string makes angle Ө with the horizontal. Find the tension T in the string and the tangential acceleration at this instant.

2. Relevant equations

3. The attempt at a solution
This is my classical mechanics homework problem.
T= Fc+W sin theta .
I have come up with this equation , is this correct . And how to find the tangential acceleration?

2. Aug 31, 2015

### Staff: Mentor

How did you come up with it, and what are Fc and W? The final answer should use R, v and Ө only.

3. Aug 31, 2015

### Hamza Abbasi

Can you show me how ?

4. Sep 1, 2015

### haruspex

m and g also.

5. Sep 1, 2015

### haruspex

Express Fc in terms of m, g, r, v, Ө (you won't need all of them). There's a standard equation you should use (and which should have been listed in the Relevant Equations).
Express W similarly.
Be careful with signs. Define whether up or down is considered positive, and whether the value of g is taken to be positive or negative. (E.g. if up is positive, then you can write gravitational acceleration as g, taking a negative value, or as -g, taking a positive value.)

6. Sep 1, 2015

### Staff: Mentor

It's not just signs, you should consider both contributions as vectors, not with their absolute values.
Right, of course.

7. Sep 1, 2015

### Hamza Abbasi

I am not getting it :(

8. Sep 1, 2015

### Staff: Mentor

At least write down the equations you know that could be relevant here, and see if one of those has quantities that are given here.

9. Sep 1, 2015

### Hamza Abbasi

And what is that relevant equation from which I should start my assumption?

10. Sep 1, 2015

### haruspex

The formula for centripetal acceleration.

11. Sep 1, 2015

### Hamza Abbasi

mv^2/r , this one? So I should substitute value of Fc in T= Fc+W sin theta? I am sorry , if my silly questions are annoying you

12. Sep 1, 2015

### haruspex

yes. Substitute for W too (mg).