# Problem with car and pendulum

1. Nov 27, 2005

### Werg22

A car takes a turn, radius = 20 m. Meanwhile a pendulum inside the car shifts 37 degree. Find the velocity of the car and find all the forces acting on the pendulum.

How to solve this? It dosen't mention from what position the pendulum starts...

2. Nov 27, 2005

### Fermat

Assume the pendulum is a bob on the end of a string.
The bob is moving in a circle of radius r = 20m.

What are the forces acting on the bob ?

3. Nov 27, 2005

### Werg22

I forgot to mention that the lenght of the string is 0.10 m... I'm affraid you got me lost...

4. Nov 27, 2005

### Fermat

You don't actually need the length of the string to answer your problem about the car's velocity.

There are only two forces acting on the bob, the weight of the bob itself, and the tension in the string.
The bob is supported vertically and the bob is moving in a circle so must have a centripetal acceleration. How does the tension in the string provide both (vertical) support for the bob and centripetal acceleration/force on the bob ?

Edit: the bob isn't supported vertically. That implies the string is straight up and down. The string is only vertical if the bob is moving in a straight line at constant velocity. Since it is moving in a circle, its inertia will tend to make it swing outwards from the vertical and away from the centre of rotation. BTW, this is a problem on centripetal force/acceleration.

Last edited: Nov 28, 2005
5. Nov 27, 2005

### Werg22

Actually I think in relationship with a passenger, I think only gravity and the tension of the string acts on the pendulum. This is like comparing the earth and a person. Well thinking of I think the question it pretty awkward. Maybe the real meaning is that the car shifts 37 degree and I only need to find the period to determine to velocity of the car. Does this seems right or not?

6. Nov 27, 2005

### lightgrav

Do you know how to add two Force vectors? That's what you have ...

Why do you think we might want to add them?

7. Nov 28, 2005

### Fermat

I amended my earlier post. Please see Edit.